From 4e9f6bd57bcfd48838bc70ee90c1ce94a161781b Mon Sep 17 00:00:00 2001
From: Tomas Bures <bures@d3s.mff.cuni.cz>
Date: Sat, 29 Jun 2019 23:19:56 +0200
Subject: [PATCH] Work in progress on refactoring all mail sending to use the
 message sender an sender workers. No yet finished.

---
 client/src/campaigns/CUD.js                   |   2 +-
 client/src/campaigns/Status.js                |  11 +-
 server/config/default.yaml                    |  15 +
 server/lib/builtin-zone-mta.js                |  92 ++--
 server/lib/knex.js                            |   6 +
 server/lib/mailers.js                         |  81 +---
 .../{campaign-sender.js => message-sender.js} | 432 ++++++++++--------
 server/lib/senders.js                         |   1 +
 server/lib/subscription-mail-helpers.js       |  26 +-
 server/lib/tools.js                           |  10 +-
 server/models/campaigns.js                    |  45 +-
 server/models/confirmations.js                |   2 +-
 server/models/subscriptions.js                |   2 +-
 server/models/templates.js                    |   2 +-
 server/models/users.js                        |  38 +-
 server/routes/archive.js                      |   4 +-
 server/services/sender-master.js              | 385 ++++++++++++----
 server/services/sender-worker.js              |  42 +-
 server/services/triggers.js                   |   6 +-
 ...neralization_of_queued_and_file_locking.js |   2 +-
 ...0190629000000_add_start_at_to_campaigns.js |  26 ++
 ...20190629170000_generalization_of_queued.js |  25 +
 22 files changed, 811 insertions(+), 444 deletions(-)
 rename server/lib/{campaign-sender.js => message-sender.js} (59%)
 create mode 100644 server/setup/knex/migrations/20190629000000_add_start_at_to_campaigns.js
 create mode 100644 server/setup/knex/migrations/20190629170000_generalization_of_queued.js

diff --git a/client/src/campaigns/CUD.js b/client/src/campaigns/CUD.js
index d0398a26..c37a195f 100644
--- a/client/src/campaigns/CUD.js
+++ b/client/src/campaigns/CUD.js
@@ -257,7 +257,7 @@ export default class CUD extends Component {
             if (this.props.entity.status === CampaignStatus.SENDING) {
                 this.disableForm();
             }
-
+            
         } else {
             const data = {};
             for (const overridable of campaignOverridables) {
diff --git a/client/src/campaigns/Status.js b/client/src/campaigns/Status.js
index 5f70fc7f..c0965af3 100644
--- a/client/src/campaigns/Status.js
+++ b/client/src/campaigns/Status.js
@@ -323,11 +323,11 @@ class SendControls extends Component {
                     </Form>
                     <ButtonRow className={campaignsStyles.sendButtonRow}>
                         {this.getFormValue('sendLater') ?
-                            <Button className="btn-primary" icon="send" label={(entity.scheduled ? t('rescheduleSend') : t('scheduleSend')) + subscrInfo} onClickAsync={::this.scheduleAsync}/>
+                            <Button className="btn-primary" icon="play" label={(entity.scheduled ? t('rescheduleSend') : t('scheduleSend')) + subscrInfo} onClickAsync={::this.scheduleAsync}/>
                             :
-                            <Button className="btn-primary" icon="send" label={t('send') + subscrInfo} onClickAsync={::this.confirmStart}/>
+                            <Button className="btn-primary" icon="play" label={t('send') + subscrInfo} onClickAsync={::this.confirmStart}/>
                         }
-                        {entity.status === CampaignStatus.PAUSED && <Button className="btn-primary" icon="refresh" label={t('reset')} onClickAsync={::this.resetAsync}/>}
+                        {entity.status === CampaignStatus.PAUSED && <Button className="btn-primary" icon="redo" label={t('reset')} onClickAsync={::this.resetAsync}/>}
                         {entity.status === CampaignStatus.PAUSED && <LinkButton className="btn-secondary" icon="signal" label={t('viewStatistics')} to={`/campaigns/${entity.id}/statistics`}/>}
                         {testButtons}
                     </ButtonRow>
@@ -341,6 +341,7 @@ class SendControls extends Component {
                         {t('Campaign is being paused. Please wait.')}
                     </AlignedRow>
                     <ButtonRow>
+                        <Button className="btn-primary" icon="pause" label={t('Pausing')} disabled={true}/>
                         <LinkButton className="btn-secondary" icon="signal" label={t('viewStatistics')} to={`/campaigns/${entity.id}/statistics`}/>
                         {testButtons}
                     </ButtonRow>
@@ -354,7 +355,7 @@ class SendControls extends Component {
                         {t('campaignIsBeingSentOut')}
                     </AlignedRow>
                     <ButtonRow>
-                        <Button className="btn-primary" icon="stop" label={t('stop')} onClickAsync={::this.stopAsync}/>
+                        <Button className="btn-primary" icon="pause" label={t('Pause')} onClickAsync={::this.stopAsync}/>
                         <LinkButton className="btn-secondary" icon="signal" label={t('viewStatistics')} to={`/campaigns/${entity.id}/statistics`}/>
                         {testButtons}
                     </ButtonRow>
@@ -371,7 +372,7 @@ class SendControls extends Component {
                     </AlignedRow>
                     <ButtonRow>
                         <Button className="btn-primary" icon="play" label={t('continue') + subscrInfo} onClickAsync={::this.confirmStart}/>
-                        <Button className="btn-primary" icon="refresh" label={t('reset')} onClickAsync={::this.resetAsync}/>
+                        <Button className="btn-primary" icon="redo" label={t('reset')} onClickAsync={::this.resetAsync}/>
                         <LinkButton className="btn-secondary" icon="signal" label={t('viewStatistics')} to={`/campaigns/${entity.id}/statistics`}/>
                         {testButtons}
                     </ButtonRow>
diff --git a/server/config/default.yaml b/server/config/default.yaml
index 6b229ab9..f400f2ef 100644
--- a/server/config/default.yaml
+++ b/server/config/default.yaml
@@ -165,6 +165,21 @@ queue:
   # How many parallel sender processes to spawn
   processes: 2
 
+  # For how long (in seconds) to try to send an email before Mailtrain stops to trying. An email can normally
+  # be sent out almost immediately. However if the send configuration is not correct or the mail server is not reachable,
+  # Mailtrain will keep retrying until the email expires.
+  # Due to Mailtrain's internal timeouts, the values should be at least 60 seconds.
+  retention:
+    # Regular and RSS campaign. Once this expires, the campaign is considered finished. The remaining recipients
+    # are included in the set of those recipients to whom the message would be delivered if the campaign is again started.
+    campaign: 86400    # 1 day
+    # Triggered campaign. Once this expires, the message gets discarded.
+    triggered: 86400   # 1 day
+    # Test send (in campaign or template)
+    test: 300          # 5 minutes
+    # Subscription and password reset related emails
+    subscription: 300  # 5 minutes
+
 cors:
   # Allow subscription widgets to be embedded
   # origins: ['https://www.example.com']
diff --git a/server/lib/builtin-zone-mta.js b/server/lib/builtin-zone-mta.js
index 06db0660..1e820f0c 100644
--- a/server/lib/builtin-zone-mta.js
+++ b/server/lib/builtin-zone-mta.js
@@ -4,17 +4,31 @@ const config = require('config');
 const fork = require('./fork').fork;
 const log = require('./log');
 const path = require('path');
-const fs = require('fs-extra')
+const fs = require('fs-extra');
 const crypto = require('crypto');
 const bluebird = require('bluebird');
 
-let zoneMtaProcess;
+let zoneMtaProcess = null;
 
 const zoneMtaDir = path.join(__dirname, '..', '..', 'zone-mta');
 const zoneMtaBuiltingConfig = path.join(zoneMtaDir, 'config', 'builtin-zonemta.json');
 
 const password = process.env.BUILTIN_ZONE_MTA_PASSWORD || crypto.randomBytes(20).toString('hex').toLowerCase();
 
+let restartCount = 0;
+let lastRestartCount = 0;
+
+let restartBackoffIdx = 0;
+const restartBackoff = [0, 30, 60, 300]; // in seconds
+
+setInterval(() => {
+    if (restartCount === lastRestartCount) {
+        restartBackoffIdx = 0;
+    }
+
+    lastRestartCount = restartCount;
+}, 300000 /* 5 mins */);
+
 function getUsername() {
     return 'mailtrain';
 }
@@ -119,36 +133,58 @@ async function createConfig() {
     await fs.writeFile(zoneMtaBuiltingConfig, JSON.stringify(cnf, null, 2));
 }
 
+function restart(callback) {
+    if (zoneMtaProcess) return callback();
+
+    if (restartCount === 0) {
+        log.info('ZoneMTA', 'Starting built-in Zone MTA process');
+    } else {
+        log.info('ZoneMTA', `Restarting built-in Zone MTA process (restart count ${restartCount})`);
+    }
+
+    zoneMtaProcess = fork(
+        path.join(zoneMtaDir, 'index.js'),
+        ['--config=' + zoneMtaBuiltingConfig],
+        {
+            cwd: zoneMtaDir,
+            env: {NODE_ENV: process.env.NODE_ENV}
+        }
+    );
+
+    zoneMtaProcess.on('message', msg => {
+        if (msg) {
+            if (msg.type === 'zone-mta-started') {
+                log.info('ZoneMTA', 'ZoneMTA process started');
+
+                if (callback) {
+                    return callback();
+                } else {
+                    return;
+                }
+            }
+        }
+    });
+
+    zoneMtaProcess.on('close', (code, signal) => {
+        log.error('ZoneMTA', 'ZoneMTA process exited with code %s signal %s', code, signal);
+
+        zoneMtaProcess = null;
+        restartCount += 1;
+
+        const backoffTimeout = restartBackoff[restartBackoffIdx] * 1000;
+        if (restartBackoffIdx < restartBackoff.length - 1) {
+            restartBackoffIdx += 1;
+        }
+
+        setTimeout(restart, backoffTimeout);
+    });
+}
+
 function spawn(callback) {
     if (config.builtinZoneMTA.enabled) {
 
         createConfig().then(() => {
-            log.info('ZoneMTA', 'Starting built-in Zone MTA process');
-
-            zoneMtaProcess = fork(
-                path.join(zoneMtaDir, 'index.js'),
-                ['--config=' + zoneMtaBuiltingConfig],
-                {
-                    cwd: zoneMtaDir,
-                    env: {NODE_ENV: process.env.NODE_ENV}
-                }
-            );
-
-            zoneMtaProcess.on('message', msg => {
-                if (msg) {
-                    if (msg.type === 'zone-mta-started') {
-                        log.info('ZoneMTA', 'ZoneMTA process started');
-                        return callback();
-                    } else if (msg.type === 'entries-added') {
-                        senders.scheduleCheck();
-                    }
-                }
-            });
-
-            zoneMtaProcess.on('close', (code, signal) => {
-                log.error('ZoneMTA', 'ZoneMTA process exited with code %s signal %s', code, signal);
-            });
-
+            restart(callback);
         }).catch(err => callback(err));
 
     } else {
diff --git a/server/lib/knex.js b/server/lib/knex.js
index 045b73cb..578fd2bd 100644
--- a/server/lib/knex.js
+++ b/server/lib/knex.js
@@ -23,6 +23,12 @@ const knex = require('knex')({
     //, debug: true
 });
 
+/*
+This is to enable logging on mysql side:
+SET GLOBAL general_log = 'ON';
+SET GLOBAL general_log_file = '/tmp/mysql-all.log';
+*/
+
 
 
 module.exports = knex;
diff --git a/server/lib/mailers.js b/server/lib/mailers.js
index e9faf41a..74a61d34 100644
--- a/server/lib/mailers.js
+++ b/server/lib/mailers.js
@@ -3,8 +3,6 @@
 const log = require('./log');
 const config = require('config');
 
-const Handlebars = require('handlebars');
-const util = require('util');
 const nodemailer = require('nodemailer');
 const aws = require('aws-sdk');
 const openpgpEncrypt = require('nodemailer-openpgp').openpgpEncrypt;
@@ -14,13 +12,21 @@ const builtinZoneMta = require('./builtin-zone-mta');
 
 const contextHelpers = require('./context-helpers');
 const settings = require('../models/settings');
-const tools = require('./tools');
-const htmlToText = require('html-to-text');
 
 const bluebird = require('bluebird');
 
 const transports = new Map();
 
+class SendConfigurationError extends Error {
+    constructor(sendConfigurationId, ...args) {
+        super(...args);
+        this.sendConfigurationId = sendConfigurationId;
+        Error.captureStackTrace(this, SendConfigurationError);
+    }
+}
+
+
+
 async function getOrCreateMailer(sendConfigurationId) {
     let sendConfiguration;
 
@@ -73,25 +79,18 @@ function _addDkimKeys(transport, mail) {
 async function _sendMail(transport, mail, template) {
     _addDkimKeys(transport, mail);
 
-    let tryCount = 0;
-    const trySend = (callback) => {
-        tryCount++;
-        transport.sendMail(mail, (err, info) => {
-            if (err) {
-                log.error('Mail', err);
-                if (err.responseCode && err.responseCode >= 400 && err.responseCode < 500 && tryCount <= 5) {
-                    // temporary error, try again
-                    log.verbose('Mail', 'Retrying after %s sec. ...', tryCount);
-                    return setTimeout(trySend, tryCount * 1000);
-                }
-                return callback(err);
-            }
-            return callback(null, info);
-        });
-    };
+    try {
+        return await transport.sendMailAsync(mail);
 
-    const trySendAsync = bluebird.promisify(trySend);
-    return await trySendAsync();
+    } catch (err) {
+        if ( (err.responseCode && err.responseCode >= 400 && err.responseCode < 500) ||
+            (err.code === 'ECONNECTION' && err.errno === 'ECONNREFUSED')
+        ) {
+            throw new SendConfigurationError(transport.mailer.sendConfiguration.id, 'Cannot connect to service specified by send configuration ' + transport.mailer.sendConfiguration.id);
+        }
+
+        throw err;
+    }
 }
 
 async function _sendTransactionalMail(transport, mail) {
@@ -103,39 +102,6 @@ async function _sendTransactionalMail(transport, mail) {
     return await _sendMail(transport, mail);
 }
 
-async function _sendTransactionalMailBasedOnTemplate(transport, mail, template) {
-    const sendConfiguration = transport.mailer.sendConfiguration;
-
-    mail.from = {
-        name: sendConfiguration.from_name,
-        address: sendConfiguration.from_email
-    };
-
-    const htmlRenderer = await tools.getTemplate(template.html, template.locale);
-
-    if (htmlRenderer) {
-        mail.html = htmlRenderer(template.data || {});
-    }
-
-    const preparedHtml = await tools.prepareHtml(mail.html);
-
-    if (preparedHtml) {
-        mail.html = preparedHtml;
-    }
-
-    const textRenderer = await tools.getTemplate(template.text, template.locale);
-
-    if (textRenderer) {
-        mail.text = textRenderer(template.data || {});
-    } else if (mail.html) {
-        mail.text = htmlToText.fromString(mail.html, {
-            wordwrap: 130
-        });
-    }
-
-    return await _sendTransactionalMail(transport, mail);
-}
-
 async function _createTransport(sendConfiguration) {
     const mailerSettings = sendConfiguration.mailer_settings;
     const mailerType = sendConfiguration.mailer_type;
@@ -222,6 +188,7 @@ async function _createTransport(sendConfiguration) {
     }
 
     const transport = nodemailer.createTransport(transportOptions, config.nodemailer);
+    transport.sendMailAsync = bluebird.promisify(transport.sendMail.bind(transport));
 
     transport.use('stream', openpgpEncrypt({
         signingKey: configItems.pgpPrivateKey,
@@ -267,8 +234,7 @@ async function _createTransport(sendConfiguration) {
     transport.mailer = {
         sendConfiguration,
         throttleWait: bluebird.promisify(throttleWait),
-        sendTransactionalMail: async (mail, template) => await _sendTransactionalMail(transport, mail),
-        sendTransactionalMailBasedOnTemplate: async (mail, template) => await _sendTransactionalMailBasedOnTemplate(transport, mail, template),
+        sendTransactionalMail: async (mail) => await _sendTransactionalMail(transport, mail),
         sendMassMail: async (mail, template) => await _sendMail(transport, mail)
     };
 
@@ -286,3 +252,4 @@ class MailerError extends Error {
 module.exports.getOrCreateMailer = getOrCreateMailer;
 module.exports.invalidateMailer = invalidateMailer;
 module.exports.MailerError = MailerError;
+module.exports.SendConfigurationError = SendConfigurationError;
\ No newline at end of file
diff --git a/server/lib/campaign-sender.js b/server/lib/message-sender.js
similarity index 59%
rename from server/lib/campaign-sender.js
rename to server/lib/message-sender.js
index 380b9bdc..f666288e 100644
--- a/server/lib/campaign-sender.js
+++ b/server/lib/message-sender.js
@@ -15,9 +15,9 @@ const links = require('../models/links');
 const {CampaignSource, CampaignType} = require('../../shared/campaigns');
 const {SubscriptionStatus} = require('../../shared/lists');
 const tools = require('./tools');
+const htmlToText = require('html-to-text');
 const request = require('request-promise');
 const files = require('../models/files');
-const htmlToText = require('html-to-text');
 const {getPublicUrl} = require('./urls');
 const blacklist = require('../models/blacklist');
 const libmime = require('libmime');
@@ -26,10 +26,11 @@ const { enforce } = require('./helpers');
 const MessageType = {
     REGULAR: 0,
     TRIGGERED: 1,
-    TEST: 2
+    TEST: 2,
+    SUBSCRIPTION: 3
 };
 
-class CampaignSender {
+class MessageSender {
     constructor() {
     }
 
@@ -40,6 +41,8 @@ class CampaignSender {
         - sendConfiguration, listId, attachments, html, text, subject
      */
     async _init(settings) {
+        this.type = settings.type;
+
         this.listsById = new Map(); // listId -> list
         this.listsByCid = new Map(); // listCid -> list
         this.listsFieldsGrouped = new Map(); // listId -> fieldsGrouped
@@ -47,11 +50,13 @@ class CampaignSender {
         await knex.transaction(async tx => {
             if (settings.campaignCid) {
                 this.campaign = await campaigns.rawGetByTx(tx, 'cid', settings.campaignCid);
+                this.isMassMail = true;
 
             } else if (settings.campaignId) {
                 this.campaign = await campaigns.rawGetByTx(tx, 'id', settings.campaignId);
+                this.isMassMail = true;
 
-            } else {
+            } else if (this.type === MessageType.TEST) {
                 // We are not within scope of a campaign (i.e. templates in MessageType.TEST message)
                 // This is to fake the campaign for getMessageLinks, which is called inside formatMessage
                 this.campaign = {
@@ -60,11 +65,15 @@ class CampaignSender {
                     from_email_override: null,
                     reply_to_override: null
                 };
+                this.isMassMail = true;
+
+            } else {
+                this.isMassMail = false;
             }
 
             if (settings.sendConfigurationId) {
                 this.sendConfiguration = await sendConfigurations.getByIdTx(tx, contextHelpers.getAdminContext(), settings.sendConfigurationId, false, true);
-            } else if (this.campaign.send_configuration) {
+            } else if (this.campaign && this.campaign.send_configuration) {
                 this.sendConfiguration = await sendConfigurations.getByIdTx(tx, contextHelpers.getAdminContext(), this.campaign.send_configuration, false, true);
             } else {
                 enforce(false);
@@ -79,7 +88,7 @@ class CampaignSender {
                 this.listsByCid.set(list.cid, list);
                 this.listsFieldsGrouped.set(list.id, await fields.listGroupedTx(tx, list.id));
 
-            } else if (this.campaign.lists) {
+            } else if (this.campaign && this.campaign.lists) {
                 for (const listSpec of this.campaign.lists) {
                     const list = await lists.getByIdTx(tx, contextHelpers.getAdminContext(), listSpec.list);
                     this.listsById.set(list.id, list);
@@ -94,7 +103,7 @@ class CampaignSender {
             if (settings.attachments) {
                 this.attachments = settings.attachments;
 
-            } else if (this.campaign.id) {
+            } else if (this.campaign && this.campaign.id) {
                 const attachments = await files.listTx(tx, contextHelpers.getAdminContext(), 'campaign', 'attachment', this.campaign.id);
 
                 this.attachments = [];
@@ -109,16 +118,21 @@ class CampaignSender {
                 this.attachments = [];
             }
 
-            if (settings.html !== undefined) {
+            if (settings.renderedHtml !== undefined) {
+                this.rendereHtml = settings.rendereHtml;
+                this.renderedText = settings.renderedText;
+
+            } else if (settings.html !== undefined) {
                 this.html = settings.html;
                 this.text = settings.text;
-            } else if (this.campaign.source === CampaignSource.TEMPLATE) {
+
+            } else if (this.campaign && this.campaign.source === CampaignSource.TEMPLATE) {
                 this.template = await templates.getByIdTx(tx, contextHelpers.getAdminContext(), this.campaign.data.sourceTemplate, false);
             }
 
             if (settings.subject !== undefined) {
                 this.subject = settings.subject;
-            } else if (this.campaign.subject !== undefined) {
+            } else if (this.campaign && this.campaign.subject !== undefined) {
                 this.subject = this.campaign.subject;
             } else {
                 enforce(false);
@@ -142,7 +156,7 @@ class CampaignSender {
             text = this.text;
             renderTags = true;
 
-        } else {
+        } else if (campaign) {
             if (campaign.source === CampaignSource.URL) {
                 const form = tools.getMessageLinks(campaign, list, subscriptionGrouped);
                 for (const key in mergeTags) {
@@ -222,14 +236,16 @@ class CampaignSender {
     }
 
     async initByCampaignCid(campaignCid) {
-        await this._init({campaignCid});
+        await this._init({type: MessageType.REGULAR, campaignCid});
     }
 
     async initByCampaignId(campaignId) {
-        await this._init({campaignId});
+        await this._init({type: MessageType.REGULAR, campaignId});
     }
 
     async getMessage(listCid, subscriptionCid) {
+        enforce(this.type === MessageType.REGULAR);
+
         const list = this.listsByCid.get(listCid);
         const subscriptionGrouped = await subscriptions.getByCid(contextHelpers.getAdminContext(), list.id, subscriptionCid);
         const flds = this.listsFieldsGrouped.get(list.id);
@@ -242,93 +258,81 @@ class CampaignSender {
 
     /*
         subData is one of:
-        - queuedMessage
+        - subscriptionId, listId, attachments
         or
         - email, listId
+        or
+        - to, subject
      */
     async _sendMessage(subData) {
-        let msgType;
-        let subscriptionGrouped;
-        let listId;
+        let msgType = this.type;
+        let to, email;
+        let envelope = false;
+        let sender = false;
+        let headers = {};
+        let listHeader = false;
+        let encryptionKeys = [];
+        let subject;
+        let message;
 
-        if (subData.queuedMessage) {
-            const queuedMessage = subData.queuedMessage;
-            msgType = queuedMessage.type;
-            listId = queuedMessage.list;
-            subscriptionGrouped = await subscriptions.getById(contextHelpers.getAdminContext(), listId, queuedMessage.subscription);
+        let subscriptionGrouped, list; // May be undefined
+        const campaign = this.campaign; // May be undefined
 
-        } else {
-            enforce(subData.email);
-            enforce(subData.listId);
+        if (subData.listId) {
+            let listId;
+            subscriptionGrouped;
 
-            msgType = MessageType.REGULAR;
-            listId = subData.listId;
-            subscriptionGrouped = await subscriptions.getByEmail(contextHelpers.getAdminContext(), listId, subData.email);
-        }
+            if (subData.subscriptionId) {
+                listId = subData.listId;
+                subscriptionGrouped = await subscriptions.getById(contextHelpers.getAdminContext(), listId, subData.subscriptionId);
 
-        const email = subscriptionGrouped.email;
-
-        if (await blacklist.isBlacklisted(email)) {
-            return;
-        }
-
-        const list = this.listsById.get(listId);
-        const flds = this.listsFieldsGrouped.get(list.id);
-        const campaign = this.campaign;
-
-        const mergeTags = fields.getMergeTags(flds, subscriptionGrouped, this._getExtraTags(campaign));
-
-        const encryptionKeys = [];
-        for (const fld of flds) {
-            if (fld.type === 'gpg' && mergeTags[fld.key]) {
-                encryptionKeys.push(mergeTags[fld.key].trim());
+            } else if (subData.email) {
+                listId = subData.listId;
+                subscriptionGrouped = await subscriptions.getByEmail(contextHelpers.getAdminContext(), listId, subData.email);
             }
-        }
 
-        const sendConfiguration = this.sendConfiguration;
+            list = this.listsById.get(listId);
+            email = subscriptionGrouped.email;
 
-        const {html, text, attachments} = await this._getMessage(list, subscriptionGrouped, mergeTags, true);
+            const flds = this.listsFieldsGrouped.get(list.id);
+            const mergeTags = fields.getMergeTags(flds, subscriptionGrouped, this._getExtraTags(campaign));
 
-        const campaignAddress = [campaign.cid, list.cid, subscriptionGrouped.cid].join('.');
-
-        let listUnsubscribe = null;
-        if (!list.listunsubscribe_disabled) {
-            listUnsubscribe = campaign.unsubscribe_url
-                ? tools.formatMessage(campaign, list, subscriptionGrouped, mergeTags, campaign.unsubscribe_url)
-                : getPublicUrl('/subscription/' + list.cid + '/unsubscribe/' + subscriptionGrouped.cid);
-        }
-
-        const mailer = await mailers.getOrCreateMailer(sendConfiguration.id);
-
-        await mailer.throttleWait();
-
-        const getOverridable = key => {
-            if (sendConfiguration[key + '_overridable'] && this.campaign[key + '_override'] !== null) {
-                return campaign[key + '_override'] || '';
-            } else {
-                return sendConfiguration[key] || '';
+            for (const fld of flds) {
+                if (fld.type === 'gpg' && mergeTags[fld.key]) {
+                    encryptionKeys.push(mergeTags[fld.key].trim());
+                }
             }
-        };
 
-        const mail = {
-            from: {
-                name: getOverridable('from_name'),
-                address: getOverridable('from_email')
-            },
-            replyTo: getOverridable('reply_to'),
-            xMailer: sendConfiguration.x_mailer ? sendConfiguration.x_mailer : false,
-            to: {
+            message = await this._getMessage(list, subscriptionGrouped, mergeTags, true);
+
+            const campaignAddress = [campaign.cid, list.cid, subscriptionGrouped.cid].join('.');
+
+            let listUnsubscribe = null;
+            if (!list.listunsubscribe_disabled) {
+                listUnsubscribe = campaign.unsubscribe_url
+                    ? tools.formatMessage(campaign, list, subscriptionGrouped, mergeTags, campaign.unsubscribe_url)
+                    : getPublicUrl('/subscription/' + list.cid + '/unsubscribe/' + subscriptionGrouped.cid);
+            }
+
+            to = {
                 name: list.to_name === null ? undefined : tools.formatMessage(campaign, list, subscriptionGrouped, mergeTags, list.to_name, false),
                 address: subscriptionGrouped.email
-            },
-            sender: this.useVerpSenderHeader ? campaignAddress + '@' + sendConfiguration.verp_hostname : false,
+            };
 
-            envelope: this.useVerp ? {
-                from: campaignAddress + '@' + sendConfiguration.verp_hostname,
-                to: subscriptionGrouped.email
-            } : false,
+            subject = tools.formatMessage(campaign, list, subscriptionGrouped, mergeTags, this.subject, false);
 
-            headers: {
+            if (this.useVerp) {
+                envelope = {
+                    from: campaignAddress + '@' + sendConfiguration.verp_hostname,
+                    to: subscriptionGrouped.email
+                };
+            }
+
+            if (this.useVerpSenderHeader) {
+                sender = campaignAddress + '@' + sendConfiguration.verp_hostname;
+            }
+
+            headers = {
                 'x-fbl': campaignAddress,
                 // custom header for SparkPost
                 'x-msys-api': JSON.stringify({
@@ -348,175 +352,237 @@ class CampaignSender {
                     prepared: true,
                     value: libmime.encodeWords(list.name) + ' <' + list.cid + '.' + getPublicUrl() + '>'
                 }
-            },
-            list: {
-                unsubscribe: listUnsubscribe
-            },
-            subject: tools.formatMessage(campaign, list, subscriptionGrouped, mergeTags, this.subject, false),
-            html,
-            text,
+            };
 
-            attachments,
+            listHeader = {
+                unsubscribe: listUnsubscribe
+            };
+
+        } else if (subData.to) {
+            to = subData.to;
+            email = to.address;
+            subject = this.subject;
+            encryptionKeys = subData.encryptionKeys;
+            message = await this._getMessage();
+        }
+
+        if (await blacklist.isBlacklisted(email)) {
+            return;
+        }
+
+        const sendConfiguration = this.sendConfiguration;
+        const mailer = await mailers.getOrCreateMailer(sendConfiguration.id);
+
+        await mailer.throttleWait();
+
+        const getOverridable = key => {
+            if (campaign && sendConfiguration[key + '_overridable'] && this.campaign[key + '_override'] !== null) {
+                return campaign[key + '_override'] || '';
+            } else {
+                return sendConfiguration[key] || '';
+            }
+        };
+
+        const mail = {
+            from: {
+                name: getOverridable('from_name'),
+                address: getOverridable('from_email')
+            },
+            replyTo: getOverridable('reply_to'),
+            xMailer: sendConfiguration.x_mailer ? sendConfiguration.x_mailer : false,
+            to,
+            sender,
+            envelope,
+            headers,
+            list: listHeader,
+            subject,
+            html: message.html,
+            text: message.text,
+            attachments: message.attachments || [],
             encryptionKeys
         };
 
 
-        let status;
         let response;
         let responseId = null;
-        try {
-            const info = await mailer.sendMassMail(mail);
-            status = SubscriptionStatus.SUBSCRIBED;
 
-            log.verbose('CampaignSender', `response: ${info.response}   messageId: ${info.messageId}`);
+        const info = this.isMassMail ? await mailer.sendMassMail(mail) : await mailer.sendTransactionalMail(mail);
 
-            let match;
-            if ((match = info.response.match(/^250 Message queued as ([0-9a-f]+)$/))) {
-                /*
-                    ZoneMTA
-                    info.response: 250 Message queued as 1691ad7f7ae00080fd
-                    info.messageId: <e65c9386-e899-7d01-b21e-ec03c3a9d9b4@sathyasai.org>
-                 */
-                response = info.response;
-                responseId = match[1];
-
-            } else if ((match = info.messageId.match(/^<([^>@]*)@.*amazonses\.com>$/))) {
-                /*
-                    AWS SES
-                    info.response: 0102016ad2244c0a-955492f2-9194-4cd1-bef9-70a45906a5a7-000000
-                    info.messageId: <0102016ad2244c0a-955492f2-9194-4cd1-bef9-70a45906a5a7-000000@eu-west-1.amazonses.com>
-                 */
-                response = info.response;
-                responseId = match[1];
-
-            } else if (info.response.match(/^250 OK$/) && (match = info.messageId.match(/^<([^>]*)>$/))) {
-                /*
-                    Postal Mail Server
-                    info.response: 250 OK
-                    info.messageId:  <xxxxxxxxx@xxx.xx> (postal messageId)
-                 */
-                response = info.response;
-                responseId = match[1];
-
-            } else {
-                /*
-                    Fallback - Mailtrain v1 behavior
-                 */
-                response = info.response || info.messageId;
-                responseId = response.split(/\s+/).pop();
-            }
-
-
-            if (msgType === MessageType.REGULAR || msgType === MessageType.TRIGGERED) {
-                await knex('campaigns').where('id', campaign.id).increment('delivered');
-            }
-        } catch (err) {
-            console.log(err);
+        log.verbose('MessageSender', `response: ${info.response}   messageId: ${info.messageId}`);
 
+        let match;
+        if ((match = info.response.match(/^250 Message queued as ([0-9a-f]+)$/))) {
             /*
-            { Error: connect ECONNREFUSED 127.0.0.1:55871
-    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1097:14)
-  cause:
-   { Error: connect ECONNREFUSED 127.0.0.1:55871
-       at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1097:14)
-     stack:
-      'Error: connect ECONNREFUSED 127.0.0.1:55871\n    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1097:14)',
-     errno: 'ECONNREFUSED',
-     code: 'ECONNECTION',
-     syscall: 'connect',
-     address: '127.0.0.1',
-     port: 55871,
-     command: 'CONN' },
-  isOperational: true,
-  errno: 'ECONNREFUSED',
-  code: 'ECONNECTION',
-  syscall: 'connect',
-  address: '127.0.0.1',
-  port: 55871,
-  command: 'CONN' }
-
+                ZoneMTA
+                info.response: 250 Message queued as 1691ad7f7ae00080fd
+                info.messageId: <e65c9386-e899-7d01-b21e-ec03c3a9d9b4@sathyasai.org>
              */
+            response = info.response;
+            responseId = match[1];
 
-            status = SubscriptionStatus.BOUNCED;
-            response = err.response || err.message;
-            if (msgType === MessageType.REGULAR || msgType === MessageType.TRIGGERED) {
-                await knex('campaigns').where('id', campaign.id).increment('delivered').increment('bounced');
-            }
+        } else if ((match = info.messageId.match(/^<([^>@]*)@.*amazonses\.com>$/))) {
+            /*
+                AWS SES
+                info.response: 0102016ad2244c0a-955492f2-9194-4cd1-bef9-70a45906a5a7-000000
+                info.messageId: <0102016ad2244c0a-955492f2-9194-4cd1-bef9-70a45906a5a7-000000@eu-west-1.amazonses.com>
+             */
+            response = info.response;
+            responseId = match[1];
+
+        } else if (info.response.match(/^250 OK$/) && (match = info.messageId.match(/^<([^>]*)>$/))) {
+            /*
+                Postal Mail Server
+                info.response: 250 OK
+                info.messageId:  <xxxxxxxxx@xxx.xx> (postal messageId)
+             */
+            response = info.response;
+            responseId = match[1];
+
+        } else {
+            /*
+                Fallback - Mailtrain v1 behavior
+             */
+            response = info.response || info.messageId;
+            responseId = response.split(/\s+/).pop();
+        }
+
+
+        if (msgType === MessageType.REGULAR || msgType === MessageType.TRIGGERED) {
+            await knex('campaigns').where('id', campaign.id).increment('delivered');
         }
 
 
         const now = new Date();
 
         if (msgType === MessageType.REGULAR) {
+            enforce(list);
+            enforce(subscriptionGrouped);
+
             await knex('campaign_messages').insert({
                 campaign: this.campaign.id,
                 list: list.id,
                 subscription: subscriptionGrouped.id,
                 send_configuration: sendConfiguration.id,
-                status,
+                status: SubscriptionStatus.SUBSCRIBED,
                 response,
                 response_id: responseId,
                 updated: now
             });
 
-        } else if (msgType === MessageType.TRIGGERED || msgType === MessageType.TEST) {
-            if (subData.queuedMessage.data.attachments) {
-                for (const attachment of subData.queuedMessage.data.attachments) {
+        } else if (msgType === MessageType.TRIGGERED || msgType === MessageType.TEST || msgType === MessageType.SUBSCRIPTION) {
+            if (subData.attachments) {
+                for (const attachment of subData.attachments) {
                     try {
                         // We ignore any errors here because we already sent the message. Thus we have to mark it as completed to avoid sending it again.
                         await knex.transaction(async tx => {
                             await files.unlockTx(tx, 'campaign', 'attachment', attachment.id);
                         });
                     } catch (err) {
-                        log.error('CampaignSender', `Error when unlocking attachment ${attachment.id} for ${listId}:${subscriptionGrouped.email} (queuedId: ${subData.queuedMessage.id})`);
+                        log.error('MessageSender', `Error when unlocking attachment ${attachment.id} for ${email} (queuedId: ${subData.queuedId})`);
                         log.verbose(err.stack);
                     }
                 }
             }
 
             await knex('queued')
-                .where({id: subData.queuedMessage.id})
+                .where({id: subData.queuedId})
                 .del();
         }
     }
 
     async sendRegularMessage(listId, email) {
+        enforce(this.type === MessageType.REGULAR);
+
         await this._sendMessage({listId, email});
     }
 }
 
-CampaignSender.sendQueuedMessage = async (queuedMessage) => {
+async function sendQueuedMessage(queuedMessage) {
     const msgData = queuedMessage.data;
 
-    const cs = new CampaignSender();
+    const cs = new MessageSender();
     await cs._init({
+        type: queuedMessage.type,
         campaignId: msgData.campaignId,
-        listId: queuedMessage.list,
+        listId: msgData.listId,
         sendConfigurationId: queuedMessage.send_configuration,
         attachments: msgData.attachments,
         html: msgData.html,
         text: msgData.text,
-        subject: msgData.subject
+        subject: msgData.subject,
+        renderedHtml: msgData.renderedHtml,
+        renderedText: msgData.renderedText
     });
 
-    await cs._sendMessage({queuedMessage});
-};
+    await cs._sendMessage({
+        subscriptionId: msgData.subscriptionId,
+        listId: msgData.listId,
+        to: msgData.to,
+        attachments: msgData.attachments,
+        encryptionKeys: msgData.encryptionKeys,
+        queuedId: queuedMessage.id
+    });
+}
 
-CampaignSender.queueMessageTx = async (tx, sendConfigurationId, listId, subscriptionId, messageType, messageData) => {
-    if (messageData.attachments) {
+async function queueCampaignMessageTx(tx, sendConfigurationId, listId, subscriptionId, messageType, messageData) {
+    enforce(messageType === MessageType.TRIGGERED || messageType === MessageType.TEST);
+
+    const msgData = {...messageData};
+
+    if (msgData.attachments) {
         for (const attachment of messageData.attachments) {
             await files.lockTx(tx,'campaign', 'attachment', attachment.id);
         }
     }
 
+    msgData.listId = listId;
+    msgData.subscriptionId = subscriptionId;
+
     await tx('queued').insert({
         send_configuration: sendConfigurationId,
-        list: listId,
-        subscription: subscriptionId,
         type: messageType,
-        data: JSON.stringify(messageData)
+        data: JSON.stringify(msgData)
     });
-};
+}
 
-module.exports.CampaignSender = CampaignSender;
-module.exports.MessageType = MessageType;
\ No newline at end of file
+async function queueSubscriptionMessage(sendConfigurationId, to, subject, encryptionKeys, template) {
+    let html, text;
+
+    const htmlRenderer = await tools.getTemplate(template.html, template.locale);
+    if (htmlRenderer) {
+        html = htmlRenderer(template.data || {});
+
+        if (html) {
+            html = await tools.prepareHtml(html);
+        }
+    }
+
+    const textRenderer = await tools.getTemplate(template.text, template.locale);
+    if (textRenderer) {
+        text = textRenderer(template.data || {});
+    } else if (html) {
+        text = htmlToText.fromString(html, {
+            wordwrap: 130
+        });
+    }
+
+    const msgData = {
+        renderedHtml: html,
+        renderedText: text,
+        to,
+        subject,
+        encryptionKeys
+    };
+
+    await tx('queued').insert({
+        send_configuration: sendConfigurationId,
+        type: MessageType.SUBSCRIPTION,
+        data: JSON.stringify(msgData)
+    });
+}
+
+module.exports.MessageSender = MessageSender;
+module.exports.MessageType = MessageType;
+module.exports.sendQueuedMessage = sendQueuedMessage;
+module.exports.queueCampaignMessageTx = queueCampaignMessageTx;
+module.exports.queueSubscriptionMessage = queueSubscriptionMessage;
diff --git a/server/lib/senders.js b/server/lib/senders.js
index 7ea15a28..476603b5 100644
--- a/server/lib/senders.js
+++ b/server/lib/senders.js
@@ -15,6 +15,7 @@ function spawn(callback) {
     log.verbose('Senders', 'Spawning master sender process');
 
     knex('campaigns').where('status', CampaignStatus.SENDING).update({status: CampaignStatus.SCHEDULED})
+    .then(() => knex('campaigns').where('status', CampaignStatus.PAUSING).update({status: CampaignStatus.PAUSED}))
     .then(() => {
         senderProcess = fork(path.join(__dirname, '..', 'services', 'sender-master.js'), [], {
             cwd: path.join(__dirname, '..'),
diff --git a/server/lib/subscription-mail-helpers.js b/server/lib/subscription-mail-helpers.js
index 838cb75c..9ffa161a 100644
--- a/server/lib/subscription-mail-helpers.js
+++ b/server/lib/subscription-mail-helpers.js
@@ -5,11 +5,10 @@ const fields = require('../models/fields');
 const settings = require('../models/settings');
 const {getTrustedUrl, getPublicUrl} = require('./urls');
 const { tUI, tMark } = require('./translate');
-const util = require('util');
 const contextHelpers = require('./context-helpers');
 const {getFieldColumn} = require('../../shared/lists');
 const forms = require('../models/forms');
-const mailers = require('./mailers');
+const messageSender = require('./message-sender');
 
 module.exports = {
     sendAlreadySubscribed,
@@ -138,20 +137,21 @@ async function _sendMail(list, email, template, locale, subjectKey, relativeUrls
 
     try {
         if (list.send_configuration) {
-            const mailer = await mailers.getOrCreateMailer(list.send_configuration);
-            await mailer.sendTransactionalMailBasedOnTemplate({
-                to: {
+            await messageSender.queueSubscriptionMessage(
+                list.send_configuration,
+                {
                     name: getDisplayName(flds, subscription),
                     address: email
                 },
-                subject: tUI(subjectKey, locale, { list: list.name }),
-                encryptionKeys
-            }, {
-                html,
-                text,
-                locale,
-                data
-            });
+                tUI(subjectKey, locale, { list: list.name }),
+                encryptionKeys,
+                {
+                    html,
+                    text,
+                    locale,
+                    data
+                }
+            );
         } else {
             log.warn('Subscription', `Not sending email for list id:${list.id} because not send configuration is set.`);
         }
diff --git a/server/lib/tools.js b/server/lib/tools.js
index 8fb0c67b..3e6f0888 100644
--- a/server/lib/tools.js
+++ b/server/lib/tools.js
@@ -42,9 +42,7 @@ async function getLocalizedFile(basePath, fileName, language) {
 }
 
 async function getTemplate(template, locale) {
-    if (!template) {
-        return false;
-    }
+    enforce(template);
 
     const key = getLangCodeFromExpressLocale(locale) + ':' + ((typeof template === 'object') ? hasher.hash(template) : template);
 
@@ -148,7 +146,7 @@ function validateEmailGetMessage(result, address, language) {
 }
 
 function formatMessage(campaign, list, subscription, mergeTags, message, isHTML) {
-    const links = getMessageLinks(campaign, list, subscription);
+    const links = campaign && list && subscription ? getMessageLinks(campaign, list, subscription) : {};
     return formatTemplate(message, links, mergeTags, isHTML);
 }
 
@@ -192,10 +190,6 @@ function formatTemplate(template, links, mergeTags, isHTML) {
 }
 
 async function prepareHtml(html) {
-    if (!(html || '').toString().trim()) {
-        return false;
-    }
-
     const { window } = new JSDOM(html);
 
     const head = window.document.querySelector('head');
diff --git a/server/models/campaigns.js b/server/models/campaigns.js
index 98a02592..7a06731d 100644
--- a/server/models/campaigns.js
+++ b/server/models/campaigns.js
@@ -17,11 +17,11 @@ const {SubscriptionStatus} = require('../../shared/lists');
 const subscriptions = require('./subscriptions');
 const segments = require('./segments');
 const senders = require('../lib/senders');
-const {LinkId} = require('./links');
+const links = require('./links');
 const feedcheck = require('../lib/feedcheck');
 const contextHelpers = require('../lib/context-helpers');
 const {convertFileURLs} = require('../lib/campaign-content');
-const {CampaignSender, MessageType} = require('../lib/campaign-sender');
+const messageSender = require('../lib/message-sender');
 const lists = require('./lists');
 
 const {EntityActivityType, CampaignActivityType} = require('../../shared/activity-log');
@@ -298,7 +298,7 @@ async function listOpensDTAjax(context, campaignId, params) {
                     return this.from('campaign_links')
                         .where('campaign_links.campaign', campaignId)
                         .where('campaign_links.list', cpgList.list)
-                        .where('campaign_links.link', LinkId.OPEN)
+                        .where('campaign_links.link', links.LinkId.OPEN)
                         .as('related_campaign_links');
                 },
                 'related_campaign_links.subscription', subsTable + '.id')
@@ -705,16 +705,12 @@ async function getMessageByCid(messageCid, withVerpHostname = false) { // withVe
 }
 
 async function getMessageByResponseId(responseId) {
-    return await knex.transaction(async tx => {
-        const message = await tx('campaign_messages')
-            .where('campaign_messages.response_id', responseId)
-            .select([
-                'campaign_messages.id', 'campaign_messages.campaign', 'campaign_messages.list', 'campaign_messages.subscription', 'campaign_messages.status'
-            ])
-            .first();
-
-        return message;
-    });
+    return await knex('campaign_messages')
+        .where('campaign_messages.response_id', responseId)
+        .select([
+            'campaign_messages.id', 'campaign_messages.campaign', 'campaign_messages.list', 'campaign_messages.subscription', 'campaign_messages.status'
+        ])
+        .first();
 }
 
 const statusFieldMapping = {
@@ -747,7 +743,6 @@ async function _changeStatusByMessageTx(tx, context, message, subscriptionStatus
 }
 
 async function changeStatusByCampaignCidAndSubscriptionIdTx(tx, context, campaignCid, listId, subscriptionId, subscriptionStatus) {
-    const campaign = await tx('campaigns').where('cid', campaignCid);
     const message = await tx('campaign_messages')
         .innerJoin('campaigns', 'campaign_messages.campaign', 'campaigns.id')
         .where('campaigns.cid', campaignCid)
@@ -856,7 +851,7 @@ async function getSubscribersQueryGeneratorTx(tx, campaignId) {
     }
 }
 
-async function _changeStatus(context, campaignId, permittedCurrentStates, newState, invalidStateMessage, scheduled = null) {
+async function _changeStatus(context, campaignId, permittedCurrentStates, newState, invalidStateMessage, startAt) {
     await knex.transaction(async tx => {
         const entity = await getByIdTx(tx, context, campaignId, false);
 
@@ -866,10 +861,18 @@ async function _changeStatus(context, campaignId, permittedCurrentStates, newSta
             throw new interoperableErrors.InvalidStateError(invalidStateMessage);
         }
 
-        await tx('campaigns').where('id', campaignId).update({
+        const updateData = {
             status: newState,
-            scheduled
-        });
+        };
+
+        if (startAt !== undefined) {
+            updateData.scheduled = startAt;
+            if (!startAt || startAt.valueOf() < Date.now()) {
+                updateData.start_at = new Date();
+            }
+        }
+
+        await tx('campaigns').where('id', campaignId).update(updateData);
 
         await activityLog.logEntityActivity('campaign', CampaignActivityType.STATUS_CHANGE, campaignId, {status: newState});
     });
@@ -929,8 +932,8 @@ async function getStatisticsOpened(context, id) {
     return await knex.transaction(async tx => {
         await shares.enforceEntityPermissionTx(tx, context, 'campaign', id, 'viewStats');
 
-        const devices = await tx('campaign_links').where('campaign', id).where('link', LinkId.OPEN).groupBy('device_type').select('device_type AS key').count('* as count');
-        const countries = await tx('campaign_links').where('campaign', id).where('link', LinkId.OPEN).groupBy('country').select('country AS key').count('* as count');
+        const devices = await tx('campaign_links').where('campaign', id).where('link', links.LinkId.OPEN).groupBy('device_type').select('device_type AS key').count('* as count');
+        const countries = await tx('campaign_links').where('campaign', id).where('link', links.LinkId.OPEN).groupBy('country').select('country AS key').count('* as count');
 
         return {
             devices,
@@ -959,7 +962,7 @@ async function testSend(context, data) {
 
     await knex.transaction(async tx => {
         const processSubscriber = async (sendConfigurationId, listId, subscriptionId, messageData) => {
-            await CampaignSender.queueMessageTx(tx, sendConfigurationId, listId, subscriptionId, MessageType.TEST, messageData);
+            await messageSender.queueCampaignMessageTx(tx, sendConfigurationId, listId, subscriptionId, messageSender.MessageType.TEST, messageData);
 
             await activityLog.logEntityActivity('campaign', CampaignActivityType.TEST_SEND, campaignId, {list: listId, subscription: subscriptionId});
         };
diff --git a/server/models/confirmations.js b/server/models/confirmations.js
index b3312bcb..f14dfd38 100644
--- a/server/models/confirmations.js
+++ b/server/models/confirmations.js
@@ -21,7 +21,7 @@ async function addConfirmation(listId, action, ip, data) {
  */
 async function takeConfirmation(cid) {
     return await knex.transaction(async tx => {
-        const entry = await tx('confirmations').select(['cid', 'list', 'action', 'ip', 'data']).where('cid', cid).first();
+        const entry = await tx('confirmations').select(['cid', 'list', 'action', 'ip', 'data']).where('cid', cid).forUpdate().first();
 
         if (!entry) {
             return false;
diff --git a/server/models/subscriptions.js b/server/models/subscriptions.js
index 3c02b0c5..4a298dd8 100644
--- a/server/models/subscriptions.js
+++ b/server/models/subscriptions.js
@@ -504,7 +504,7 @@ async function serverValidate(context, listId, data) {
 async function _validateAndPreprocess(tx, listId, groupedFieldsMap, entity, meta, isCreate) {
     enforce(entity.email, 'Email must be set');
 
-    const existingWithKeyQuery = tx(getSubscriptionTableName(listId)).where('hash_email', hashEmail(entity.email));
+    const existingWithKeyQuery = tx(getSubscriptionTableName(listId)).where('hash_email', hashEmail(entity.email)).forUpdate();
 
     if (!isCreate) {
         existingWithKeyQuery.whereNot('id', entity.id);
diff --git a/server/models/templates.js b/server/models/templates.js
index c04b2cca..cd7c22ca 100644
--- a/server/models/templates.js
+++ b/server/models/templates.js
@@ -153,7 +153,7 @@ async function remove(context, id) {
 
 const MAX_EMAIL_COUNT = 100;
 async function sendAsTransactionalEmail(context, templateId, sendConfigurationId, emails, subject, mergeTags) {
-    // TODO - Update this to use CampaignSender.queueMessageTx (with renderedHtml and renderedText)
+    // TODO - Update this to use MessageSender.queueMessageTx (with renderedHtml and renderedText)
 
     if (emails.length > MAX_EMAIL_COUNT) {
         throw new Error(`Cannot send more than ${MAX_EMAIL_COUNT} emails at once`);
diff --git a/server/models/users.js b/server/models/users.js
index 038fc045..b35ceaae 100644
--- a/server/models/users.js
+++ b/server/models/users.js
@@ -12,6 +12,8 @@ const crypto = require('crypto');
 const settings = require('./settings');
 const {getTrustedUrl} = require('../lib/urls');
 const { tUI } = require('../lib/translate');
+const messageSender = require('../lib/message-sender');
+const {getSystemSendConfigurationId} = require('../../shared/send-configurations');
 
 const bluebird = require('bluebird');
 
@@ -19,8 +21,6 @@ const bcrypt = require('bcrypt-nodejs');
 const bcryptHash = bluebird.promisify(bcrypt.hash.bind(bcrypt));
 const bcryptCompare = bluebird.promisify(bcrypt.compare.bind(bcrypt));
 
-const mailers = require('../lib/mailers');
-
 const passport = require('../lib/passport');
 
 const namespaceHelpers = require('../lib/namespace-helpers');
@@ -297,26 +297,31 @@ async function resetAccessToken(userId) {
 async function sendPasswordReset(locale, usernameOrEmail) {
     enforce(passport.isAuthMethodLocal, 'Local user management is required');
 
+    const resetToken = crypto.randomBytes(16).toString('base64').replace(/[^a-z0-9]/gi, '');
+    let user;
+
     await knex.transaction(async tx => {
-        const user = await tx('users').where('username', usernameOrEmail).orWhere('email', usernameOrEmail).select(['id', 'username', 'email', 'name']).first();
+        user = await tx('users').where('username', usernameOrEmail).orWhere('email', usernameOrEmail).select(['id', 'username', 'email', 'name']).forUpdate().first();
 
         if (user) {
-            const resetToken = crypto.randomBytes(16).toString('base64').replace(/[^a-z0-9]/gi, '');
-
             await tx('users').where('id', user.id).update({
                 reset_token: resetToken,
                 reset_expire: new Date(Date.now() + 60 * 60 * 1000)
             });
+        }
+        // We intentionally silently ignore the situation when user is not found. This is not to reveal if a user exists in the system.
 
-            const { adminEmail } = await settings.get(contextHelpers.getAdminContext(), ['adminEmail']);
+    });
 
-            const mailer = await mailers.getOrCreateMailer();
-            await mailer.sendTransactionalMailBasedOnTemplate({
-                to: {
-                    address: user.email
-                },
-                subject: tUI('mailerPasswordChangeRequest', locale)
-            }, {
+    if (user) {
+        await messageSender.queueSubscriptionMessage(
+            getSystemSendConfigurationId(),
+            {
+                address: user.email
+            },
+            tUI('mailerPasswordChangeRequest', locale),
+            null,
+            {
                 html: 'users/password-reset-html.hbs',
                 text: 'users/password-reset-text.hbs',
                 locale,
@@ -326,10 +331,9 @@ async function sendPasswordReset(locale, usernameOrEmail) {
                     name: user.name,
                     confirmUrl: getTrustedUrl(`login/reset/${encodeURIComponent(user.username)}/${encodeURIComponent(resetToken)}`)
                 }
-            });
-        }
-        // We intentionally silently ignore the situation when user is not found. This is not to reveal if a user exists in the system.
-    });
+            }
+        );
+    }
 }
 
 async function isPasswordResetTokenValid(username, resetToken) {
diff --git a/server/routes/archive.js b/server/routes/archive.js
index 566fa146..10b602d8 100644
--- a/server/routes/archive.js
+++ b/server/routes/archive.js
@@ -1,11 +1,11 @@
 'use strict';
 
 const router = require('../lib/router-async').create();
-const {CampaignSender} = require('../lib/campaign-sender');
+const {MessageSender} = require('../lib/message-sender');
 
 
 router.get('/:campaign/:list/:subscription', (req, res, next) => {
-    const cs = new CampaignSender();
+    const cs = new MessageSender();
     cs.initByCampaignCid(req.params.campaign)
         .then(() => cs.getMessage(req.params.list, req.params.subscription))
         .then(result => {
diff --git a/server/services/sender-master.js b/server/services/sender-master.js
index 05f4aaf5..36fc5b8b 100644
--- a/server/services/sender-master.js
+++ b/server/services/sender-master.js
@@ -10,7 +10,7 @@ const campaigns = require('../models/campaigns');
 const builtinZoneMta = require('../lib/builtin-zone-mta');
 const {CampaignActivityType} = require('../../shared/activity-log');
 const activityLog = require('../lib/activity-log');
-const {MessageType} = require('../lib/campaign-sender')
+const {MessageType} = require('../lib/message-sender');
 require('../lib/fork');
 
 class Notifications {
@@ -55,19 +55,111 @@ const idleWorkers = [];
 let campaignSchedulerRunning = false;
 let queuedSchedulerRunning = false;
 
-const campaignsCheckPeriod = 30 * 1000;
+const checkPeriod = 30 * 1000;
 const retrieveBatchSize = 1000;
 const workerBatchSize = 10;
 
+const sendConfigurationIdByCampaignId = new Map(); // campaignId -> sendConfigurationId
+const sendConfigurationStatuses = new Map(); // sendConfigurationId -> {retryCount, postponeTill}
+
 const sendConfigurationMessageQueue = new Map(); // sendConfigurationId -> [{queuedMessage}]
 const campaignMessageQueue = new Map(); // campaignId -> [{listId, email}]
 
-const workAssignment = new Map(); // workerId -> { campaignId, messages: [{listId, email} } / { sendConfigurationId, messages: [{queuedMessage}] }
+const workAssignment = new Map(); // workerId -> { type: WorkAssignmentType.CAMPAIGN, campaignId, messages: [{listId, email} } / { type: WorkAssignmentType.QUEUED, sendConfigurationId, messages: [{queuedMessage}] }
+
+const WorkAssignmentType = {
+    CAMPAIGN: 0,
+    QUEUED: 1
+};
+
+const retryBackoff = [10, 20, 30, 30, 60, 60, 120, 120, 300]; // in seconds
+
+function getSendConfigurationStatus(sendConfigurationId) {
+    let status = sendConfigurationStatuses.get(sendConfigurationId);
+    if (!status) {
+        status = {
+            retryCount: 0,
+            postponeTill: 0
+        };
+
+        sendConfigurationStatuses.set(sendConfigurationId, status);
+    }
+
+    return status;
+}
+
+function setSendConfigurationRetryCount(sendConfigurationStatus, newRetryCount) {
+    sendConfigurationStatus.retryCount = newRetryCount;
+
+    let next = 0;
+    if (newRetryCount > 0) {
+        let backoff;
+        if (newRetryCount > retryBackoff.length) {
+            backoff = retryBackoff[retryBackoff.length - 1];
+        } else {
+            backoff = retryBackoff[newRetryCount - 1];
+        }
+
+        next = Date.now() + backoff * 1000;
+        setTimeout(scheduleCheck, backoff * 1000);
+    }
+
+    sendConfigurationStatus.postponeTill = next;
+}
+
+function isSendConfigurationPostponed(sendConfigurationId) {
+    const now = Date.now();
+    const sendConfigurationStatus = getSendConfigurationStatus(sendConfigurationId);
+    return sendConfigurationStatus.postponeTill > now;
+}
+
+function getPostponedSendConfigurationIds() {
+    const result = [];
+    const now = Date.now();
+
+    for (const entry of sendConfigurationStatuses.entries()) {
+        if (entry[1].postponeTill > now) {
+            result.push(entry[0]);
+        }
+    }
+
+    return result;
+}
 
 
-function messagesProcessed(workerId) {
+function getExpirationThresholds() {
+    const now = Date.now();
+
+    return {
+        [MessageType.TRIGGERED]: {
+            threshold: now - config.queue.retention.triggered * 1000,
+            title: 'triggered campaign'
+        },
+        [MessageType.TEST]: {
+            threshold: now - config.queue.retention.test * 1000,
+            title: 'test campaign'
+        },
+        [MessageType.SUBSCRIPTION]: {
+            threshold: now - config.queue.retention.subscription * 1000,
+            title: 'subscription and password-related'
+        }
+    };
+}
+
+
+function messagesProcessed(workerId, withErrors) {
     const wa = workAssignment.get(workerId);
 
+    const sendConfigurationStatus = getSendConfigurationStatus(wa.sendConfigurationId);
+    if (withErrors) {
+        if (sendConfigurationStatus.retryCount === wa.sendConfigurationRetryCount) { // This is to avoid multiple increments when more workers simultaneously fail to send messages ot the same send configuration
+            setSendConfigurationRetryCount(sendConfigurationStatus, sendConfigurationStatus.retryCount + 1);
+        }
+    } else {
+        setSendConfigurationRetryCount(sendConfigurationStatus, 0);
+    }
+
+
     workAssignment.delete(workerId);
     idleWorkers.push(workerId);
 
@@ -75,8 +167,6 @@ function messagesProcessed(workerId) {
 }
 
 async function workersLoop() {
-    const reservedWorkersForTestCount = workersCount > 1 ? 1 : 0;
-
     async function getAvailableWorker() {
         while (idleWorkers.length === 0) {
             await notifier.waitFor('workerFinished');
@@ -85,64 +175,42 @@ async function workersLoop() {
         return idleWorkers.shift();
     }
 
-    function assignCampaignTaskToWorker(workerId, task) {
-        const campaignId = task.campaignId;
-        const queue = task.queue;
-
-        const messages = queue.splice(0, workerBatchSize);
-        workAssignment.set(workerId, {campaignId, messages});
-
-        if (queue.length === 0) {
-            notifier.notify(`campaignMessageQueueEmpty:${campaignId}`);
-        }
-
-        sendToWorker(workerId, 'process-campaign-messages', {
-            campaignId,
-            messages
-        });
-    }
-
-    function assignSendConfigurationTaskToWorker(workerId, task) {
-        const sendConfigurationId = task.sendConfigurationId;
-        const queue = task.queue;
-
-        const messages = queue.splice(0, workerBatchSize);
-        workAssignment.set(workerId, {sendConfigurationId, messages});
-
-        if (queue.length === 0) {
-            notifier.notify(`sendConfigurationMessageQueueEmpty:${sendConfigurationId}`);
-        }
-
-        sendToWorker(workerId, 'process-queued-messages', {
-            sendConfigurationId,
-            messages
-        });
-    }
-
     function selectNextTask() {
         const allocationMap = new Map();
         const allocation = [];
 
-        function initAllocation(attrName, queues, assignWorkerHandler) {
+        function initAllocation(waType, attrName, queues, workerMsg, getSendConfigurationId, getQueueEmptyEvent) {
             for (const id of queues.keys()) {
+                const sendConfigurationId = getSendConfigurationId(id);
                 const key = attrName + ':' + id;
 
                 const queue = queues.get(id);
 
+                const postponed = isSendConfigurationPostponed(sendConfigurationId);
+
                 const task = {
-                    [attrName]: id,
+                    type: waType,
+                    id,
                     existingWorkers: 0,
-                    isEmpty: queue.length === 0,
+                    isValid: queue.length > 0 && !postponed,
                     queue,
-                    assignWorkerHandler
+                    workerMsg,
+                    attrName,
+                    getQueueEmptyEvent,
+                    sendConfigurationId
                 };
 
                 allocationMap.set(key, task);
                 allocation.push(task);
+
+                if (postponed && queue.length > 0) {
+                    queue.splice(0);
+                    notifier.notify(task.getQueueEmptyEvent(task));
+                }
             }
 
             for (const wa of workAssignment.values()) {
-                if (wa[attrName]) {
+                if (wa.type === waType) {
                     const key = attrName + ':' + wa[attrName];
                     const task = allocationMap.get(key);
                     task.existingWorkers += 1;
@@ -150,14 +218,29 @@ async function workersLoop() {
             }
         }
 
-        initAllocation('sendConfigurationId', sendConfigurationMessageQueue, assignSendConfigurationTaskToWorker);
-        initAllocation('campaignId', campaignMessageQueue, assignCampaignTaskToWorker);
+        initAllocation(
+            WorkAssignmentType.QUEUED,
+            'sendConfigurationId',
+            sendConfigurationMessageQueue,
+            'process-queued-messages',
+                id => id,
+                task => `sendConfigurationMessageQueueEmpty:${task.id}`
+        );
+
+        initAllocation(
+            WorkAssignmentType.CAMPAIGN,
+            'campaignId',
+            campaignMessageQueue,
+            'process-campaign-messages',
+                id => sendConfigurationIdByCampaignId.get(id),
+            task => `campaignMessageQueueEmpty:${task.id}`
+        );
 
         let minTask = null;
         let minExistingWorkers;
 
         for (const task of allocation) {
-            if (!task.isEmpty && (minTask === null || minExistingWorkers > task.existingWorkers)) {
+            if (task.isValid && (minTask === null || minExistingWorkers > task.existingWorkers)) {
                 minTask = task;
                 minExistingWorkers = task.existingWorkers;
             }
@@ -172,8 +255,31 @@ async function workersLoop() {
 
         if (task) {
             const workerId = await getAvailableWorker();
-            task.assignWorkerHandler(workerId, task);
-            
+
+            const attrName = task.attrName;
+            const sendConfigurationId = task.sendConfigurationId;
+            const sendConfigurationStatus = getSendConfigurationStatus(sendConfigurationId);
+            const sendConfigurationRetryCount = sendConfigurationStatus.retryCount;
+
+            const queue = task.queue;
+
+            const messages = queue.splice(0, workerBatchSize);
+            workAssignment.set(workerId, {
+                type: task.type,
+                [attrName]: task.id,
+                sendConfigurationId,
+                sendConfigurationRetryCount,
+                messages
+            });
+
+            if (queue.length === 0) {
+                notifier.notify(task.getQueueEmptyEvent(task));
+            }
+
+            sendToWorker(workerId, task.workerMsg, {
+                [attrName]: task.id,
+                messages
+            });
         } else {
             await notifier.waitFor('workAvailable');
         }
@@ -184,14 +290,18 @@ async function workersLoop() {
 async function processCampaign(campaignId) {
     const msgQueue = campaignMessageQueue.get(campaignId);
 
-    async function finish(newStatus) {
+    async function finish(clearMsgQueue, newStatus) {
+        if (clearMsgQueue) {
+            msgQueue.splice(0);
+        }
+
         const isCompleted = () => {
             if (msgQueue.length > 0) return false;
 
             let workerRunning = false;
 
             for (const wa of workAssignment.values()) {
-                if (wa.campaignId === campaignId) {
+                if (wa.type === WorkAssignmentType.CAMPAIGN && wa.campaignId === campaignId) {
                     workerRunning = true;
                 }
             }
@@ -213,10 +323,20 @@ async function processCampaign(campaignId) {
         while (true) {
             const cpg = await knex('campaigns').where('id', campaignId).first();
 
+            const expirationThreshold = Date.now() - config.queue.retention.campaign * 1000;
+            if (cpg.start_at.valueOf() < expirationThreshold) {
+                return await finish(true, CampaignStatus.FINISHED);
+            }
+
             if (cpg.status === CampaignStatus.PAUSING) {
-                msgQueue.splice(0);
-                await finish(CampaignStatus.PAUSED);
-                return;
+                return await finish(true, CampaignStatus.PAUSED);
+            }
+
+            sendConfigurationIdByCampaignId.set(cpg.id, cpg.send_configuration);
+
+            if (isSendConfigurationPostponed(cpg.send_configuration)) {
+                // postpone campaign if its send configuration is problematic
+                return await finish(true, CampaignStatus.SCHEDULED);
             }
 
             let qryGen;
@@ -227,7 +347,7 @@ async function processCampaign(campaignId) {
             if (qryGen) {
                 let messagesInProcessing = [...msgQueue];
                 for (const wa of workAssignment.values()) {
-                    if (wa.campaignId === campaignId) {
+                    if (wa.type === WorkAssignmentType.CAMPAIGN && wa.campaignId === campaignId) {
                         messagesInProcessing = messagesInProcessing.concat(wa.messages);
                     }
                 }
@@ -239,8 +359,7 @@ async function processCampaign(campaignId) {
                 const subs = await qry;
 
                 if (subs.length === 0) {
-                    await finish(CampaignStatus.FINISHED);
-                    return;
+                    return await finish(false, CampaignStatus.FINISHED);
                 }
 
                 for (const sub of subs) {
@@ -257,8 +376,7 @@ async function processCampaign(campaignId) {
                 }
 
             } else {
-                await finish(CampaignStatus.FINISHED);
-                return;
+                return await finish(false, CampaignStatus.FINISHED);
             }
         }
     } catch (err) {
@@ -276,15 +394,29 @@ async function scheduleCampaigns() {
     campaignSchedulerRunning = true;
 
     try {
+        // finish old campaigns
+        const nowDate = new Date();
+        const now = nowDate.valueOf();
+
+        const expirationThreshold = new Date(now - config.queue.retention.campaign * 1000);
+        const expiredCampaigns = await knex('campaigns')
+            .whereIn('campaigns.type', [CampaignType.REGULAR, CampaignType.RSS_ENTRY])
+            .whereIn('campaigns.status', [CampaignStatus.SCHEDULED, CampaignStatus.PAUSED])
+            .where('campaigns.start_at', '<', expirationThreshold)
+            .update({status: CampaignStatus.FINISHED});
+
         while (true) {
             let campaignId = 0;
+            const postponedSendConfigurationIds = getPostponedSendConfigurationIds();
 
             await knex.transaction(async tx => {
                 const scheduledCampaign = await tx('campaigns')
                     .whereIn('campaigns.type', [CampaignType.REGULAR, CampaignType.RSS_ENTRY])
+                    .whereNotIn('campaigns.send_configuration', postponedSendConfigurationIds)
                     .where('campaigns.status', CampaignStatus.SCHEDULED)
-                    .where(qry => qry.whereNull('campaigns.scheduled').orWhere('campaigns.scheduled', '<=', new Date()))
+                    .where('campaigns.start_at', '<=', nowDate)
                     .select(['id'])
+                    .forUpdate()
                     .first();
 
                 if (scheduledCampaign) {
@@ -322,7 +454,7 @@ async function processQueuedBySendConfiguration(sendConfigurationId) {
         let workerRunning = false;
 
         for (const wa of workAssignment.values()) {
-            if (wa.sendConfigurationId === sendConfigurationId) {
+            if (wa.type === WorkAssignmentType.QUEUED && wa.sendConfigurationId === sendConfigurationId) {
                 workerRunning = true;
             }
         }
@@ -330,19 +462,40 @@ async function processQueuedBySendConfiguration(sendConfigurationId) {
         return !workerRunning;
     };
 
+    async function finish(clearMsgQueue, deleteMsgQueue) {
+        if (clearMsgQueue) {
+            msgQueue.splice(0);
+        }
+
+        while (!isCompleted()) {
+            await notifier.waitFor('workerFinished');
+        }
+
+        if (deleteMsgQueue) {
+            sendConfigurationMessageQueue.delete(sendConfigurationId);
+        }
+    }
+
+
     try {
         while (true) {
+            if (isSendConfigurationPostponed(sendConfigurationId)) {
+                return finish(true, true);
+            }
+
             let messagesInProcessing = [...msgQueue];
             for (const wa of workAssignment.values()) {
-                if (wa.sendConfigurationId === sendConfigurationId) {
+                if (wa.type === WorkAssignmentType.QUEUED && wa.sendConfigurationId === sendConfigurationId) {
                     messagesInProcessing = messagesInProcessing.concat(wa.messages);
                 }
             }
 
+            const messageIdsInProcessing = messagesInProcessing.map(x => x.queuedMessage.id);
+
             const rows = await knex('queued')
-                .orderByRaw(`FIELD(type, ${MessageType.TRIGGERED}, ${MessageType.TEST}) DESC, id ASC`) // This orders MessageType.TEST messages before MessageType.TRIGGERED ones
+                .orderByRaw(`FIELD(type, ${MessageType.TRIGGERED}, ${MessageType.TEST}, ${MessageType.SUBSCRIPTION}) DESC, id ASC`) // This orders messages in the following order MessageType.SUBSCRIPTION, MessageType.TEST and MessageType.TRIGGERED
                 .where('send_configuration', sendConfigurationId)
-                .whereNotIn('id', messagesInProcessing.map(x => x.queuedMessage.id))
+                .whereNotIn('id', messageIdsInProcessing)
                 .limit(retrieveBatchSize);
 
             if (rows.length === 0) {
@@ -351,20 +504,43 @@ async function processQueuedBySendConfiguration(sendConfigurationId) {
                     return;
 
                 } else {
-                    while (!isCompleted()) {
-                        await notifier.waitFor('workerFinished');
-                    }
+                    finish(false, false);
 
                     // At this point, there might be new messages in the queued that could belong to us. Thus we have to try again instead for returning.
                     continue;
                 }
             }
 
+            const expirationThresholds = getExpirationThresholds();
+            const expirationCounters = {};
+            for (const type of Object.keys(expirationThresholds)) {
+                expirationCounters[type] = 0;
+            }
+
             for (const row of rows) {
-                row.data = JSON.parse(row.data);
-                msgQueue.push({
-                    queuedMessage: row
-                });
+                for (const type of Object.keys(expirationThresholds)) {
+                    if (row.type === type) {
+                        const expirationThreshold = expirationThresholds[type];
+
+                        if (row.created < expirationThreshold.threshold) {
+                            expirationCounters[type] += 1;
+                            await knex('queued').where('id', row.id).del();
+
+                        } else {
+                            row.data = JSON.parse(row.data);
+                            msgQueue.push({
+                                queuedMessage: row
+                            });
+                        }
+                    }
+                }
+            }
+
+            for (const type of Object.keys(expirationThresholds)) {
+                const expirationThreshold = expirationThresholds[type];
+                if (expirationCounters[type] > 0) {
+                    log.warn('Senders', `Discarded ${expirationCounters[type]} expired ${expirationThreshold.title} message(s).`);
+                }
             }
 
             notifier.notify('workAvailable');
@@ -387,22 +563,37 @@ async function scheduleQueued() {
     queuedSchedulerRunning = true;
 
     try {
-        while (true) {
-            const sendConfigurationsInProcessing = [...sendConfigurationMessageQueue.keys()];
+        const sendConfigurationsIdsInProcessing = [...sendConfigurationMessageQueue.keys()];
+        const postponedSendConfigurationIds = getPostponedSendConfigurationIds();
 
-            const rows = await knex('queued')
-                .whereNotIn('send_configuration', sendConfigurationsInProcessing)
-                .groupBy('send_configuration')
-                .select(['send_configuration']);
+        // prune old messages
+        const expirationThresholds = getExpirationThresholds();
+        for (const type of Object.keys(expirationThresholds)) {
+            const expirationThreshold = expirationThresholds[type];
 
-            for (const row of rows) {
-                const sendConfigurationId = row.send_configuration;
-                sendConfigurationMessageQueue.set(sendConfigurationId, []);
+            const expiredCount = await knex('queued')
+                .whereNotIn('send_configuration', sendConfigurationsIdsInProcessing)
+                .where('type', type)
+                .where('created', '<', expirationThreshold.threshold)
+                .del();
 
-                // noinspection JSIgnoredPromiseFromCall
-                processQueuedBySendConfiguration(sendConfigurationId);
+            if (expiredCount) {
+                log.warn('Senders', `Discarded ${expiredCount} expired ${expirationThreshold.title} message(s).`);
             }
         }
+
+        const rows = await knex('queued')
+            .whereNotIn('send_configuration', [...sendConfigurationsIdsInProcessing, ...postponedSendConfigurationIds])
+            .groupBy('send_configuration')
+            .select(['send_configuration']);
+
+        for (const row of rows) {
+            const sendConfigurationId = row.send_configuration;
+            sendConfigurationMessageQueue.set(sendConfigurationId, []);
+
+            // noinspection JSIgnoredPromiseFromCall
+            processQueuedBySendConfiguration(sendConfigurationId);
+        }
     } catch (err) {
         log.error('Senders', `Scheduling queued messages failed with error: ${err.message}`);
         log.verbose(err.stack);
@@ -431,7 +622,7 @@ async function spawnWorker(workerId) {
                     return resolve();
 
                 } else if (msg.type === 'messages-processed') {
-                    messagesProcessed(workerId);
+                    messagesProcessed(workerId, msg.data.withErrors);
                 }
 
             }
@@ -457,16 +648,22 @@ function sendToWorker(workerId, msgType, data) {
 }
 
 
-function periodicCampaignsCheck() {
+function scheduleCheck() {
     // noinspection JSIgnoredPromiseFromCall
     scheduleCampaigns();
 
     // noinspection JSIgnoredPromiseFromCall
     scheduleQueued();
-
-    setTimeout(periodicCampaignsCheck, campaignsCheckPeriod);
 }
 
+function periodicCheck() {
+    // noinspection JSIgnoredPromiseFromCall
+    scheduleCheck();
+
+    setTimeout(periodicCheck, checkPeriod);
+}
+
+
 async function init() {
     const spawnWorkerFutures = [];
     let workerId;
@@ -482,10 +679,18 @@ async function init() {
 
             if (type === 'schedule-check') {
                 // noinspection JSIgnoredPromiseFromCall
-                scheduleCampaigns();
-                scheduleQueued();
+                scheduleCheck();
 
             } else if (type === 'reload-config') {
+                const sendConfigurationStatus = getSendConfigurationStatus(msg.data.sendConfigurationId);
+                if (sendConfigurationStatus.retryCount > 0) {
+                    const sendConfigurationStatus = getSendConfigurationStatus(msg.data.sendConfigurationId)
+                    setSendConfigurationRetryCount(sendConfigurationStatus, 0);
+
+                    // noinspection JSIgnoredPromiseFromCall
+                    scheduleCheck();
+                }
+
                 for (const workerId of workerProcesses.keys()) {
                     sendToWorker(workerId, 'reload-config', msg.data);
                 }
@@ -501,7 +706,7 @@ async function init() {
         type: 'master-sender-started'
     });
 
-    periodicCampaignsCheck();
+    periodicCheck();
 
     setImmediate(workersLoop);
 }
diff --git a/server/services/sender-worker.js b/server/services/sender-worker.js
index a9f4c3d8..ff830adb 100644
--- a/server/services/sender-worker.js
+++ b/server/services/sender-worker.js
@@ -3,7 +3,7 @@
 const config = require('config');
 const log = require('../lib/log');
 const mailers = require('../lib/mailers');
-const {CampaignSender} = require('../lib/campaign-sender');
+const messageSender = require('../lib/message-sender');
 require('../lib/fork');
 
 const workerId = Number.parseInt(process.argv[2]);
@@ -17,23 +17,33 @@ async function processCampaignMessages(campaignId, messages) {
 
     running = true;
 
-    const cs = new CampaignSender();
+    const cs = new MessageSender();
     await cs.initByCampaignId(campaignId);
 
+    let withErrors = false;
+
     for (const msgData of messages) {
         try {
             await cs.sendRegularMessage(msgData.listId, msgData.email);
 
             log.verbose('Senders', 'Message sent and status updated for %s:%s', msgData.listId, msgData.email);
         } catch (err) {
-            log.error('Senders', `Sending message to ${msgData.listId}:${msgData.email} failed with error: ${err.message}`);
-            log.verbose(err.stack);
+
+            if (err instanceof mailers.SendConfigurationError) {
+                log.error('Senders', `Sending message to ${msgData.listId}:${msgData.email} failed with error: ${err.message}. Will retry the message if within retention interval.`);
+                withErrors = true;
+                break;
+
+            } else {
+                log.error('Senders', `Sending message to ${msgData.listId}:${msgData.email} failed with error: ${err.message}. Dropping the message.`);
+                log.verbose(err.stack);
+            }
         }
     }
 
     running = false;
 
-    sendToMaster('messages-processed');
+    sendToMaster('messages-processed', { withErrors });
 }
 
 async function processQueuedMessages(sendConfigurationId, messages) {
@@ -44,26 +54,34 @@ async function processQueuedMessages(sendConfigurationId, messages) {
 
     running = true;
 
+    let withErrors = false;
+
     for (const msgData of messages) {
         const queuedMessage = msgData.queuedMessage;
         try {
-            await CampaignSender.sendQueuedMessage(queuedMessage);
-
+            await messageSender.sendQueuedMessage(queuedMessage);
             log.verbose('Senders', 'Message sent and status updated for %s:%s', queuedMessage.list, queuedMessage.subscription);
         } catch (err) {
-            log.error('Senders', `Sending message to ${queuedMessage.list}:${queuedMessage.subscription} failed with error: ${err.message}`);
-            log.verbose(err.stack);
+            if (err instanceof mailers.SendConfigurationError) {
+                log.error('Senders', `Sending message to ${queuedMessage.list}:${queuedMessage.subscription} failed with error: ${err.message}. Will retry the message if within retention interval.`);
+                withErrors = true;
+                break;
+            } else {
+                log.error('Senders', `Sending message to ${queuedMessage.list}:${queuedMessage.subscription} failed with error: ${err.message}. Dropping the message.`);
+                log.verbose(err.stack);
+            }
         }
     }
 
     running = false;
 
-    sendToMaster('messages-processed');
+    sendToMaster('messages-processed', { withErrors });
 }
 
-function sendToMaster(msgType) {
+function sendToMaster(msgType, data) {
     process.send({
-        type: msgType
+        type: msgType,
+        data
     });
 }
 
diff --git a/server/services/triggers.js b/server/services/triggers.js
index 3689f425..0eb58ee3 100644
--- a/server/services/triggers.js
+++ b/server/services/triggers.js
@@ -10,7 +10,7 @@ const { Entity, Event } = require('../../shared/triggers');
 const { SubscriptionStatus } = require('../../shared/lists');
 const links = require('../models/links');
 const contextHelpers = require('../lib/context-helpers');
-const {MessageType, CampaignSender} = require('../lib/campaign-sender');
+const messageSender = require('../lib/message-sender');
 
 const triggerCheckPeriod = 30 * 1000;
 const triggerFirePeriod = 120 * 1000;
@@ -152,8 +152,8 @@ async function run() {
                         subscription: subscriber.id
                     });
 
-                    await CampaignSender.queueMessageTx(tx,
-                        campaign.send_configuration, cpgList.list, subscriber.id, MessageType.TRIGGERED,
+                    await messageSender.queueCampaignMessageTx(tx,
+                        campaign.send_configuration, cpgList.list, subscriber.id, messageSender.MessageType.TRIGGERED,
                         {
                             campaignId: campaign.id,
                             triggerId: trigger.id
diff --git a/server/setup/knex/migrations/20190615000000_generalization_of_queued_and_file_locking.js b/server/setup/knex/migrations/20190615000000_generalization_of_queued_and_file_locking.js
index 99b2c6d1..e479e653 100644
--- a/server/setup/knex/migrations/20190615000000_generalization_of_queued_and_file_locking.js
+++ b/server/setup/knex/migrations/20190615000000_generalization_of_queued_and_file_locking.js
@@ -15,7 +15,7 @@ const entityTypesWithFiles = {
 exports.up = (knex, Promise) => (async() => {
     await knex.schema.table('queued', table => {
         table.integer('send_configuration').unsigned().notNullable();
-        table.integer('type').unsigned().notNullable(); // The values come from campaign-sender.js:MessageType
+        table.integer('type').unsigned().notNullable(); // The values come from message-sender.js:MessageType
         table.text('data', 'longtext');
     });
 
diff --git a/server/setup/knex/migrations/20190629000000_add_start_at_to_campaigns.js b/server/setup/knex/migrations/20190629000000_add_start_at_to_campaigns.js
new file mode 100644
index 00000000..593885b9
--- /dev/null
+++ b/server/setup/knex/migrations/20190629000000_add_start_at_to_campaigns.js
@@ -0,0 +1,26 @@
+const { CampaignType, CampaignStatus } = require('../../../../shared/campaigns');
+
+exports.up = (knex, Promise) => (async() => {
+    await knex.schema.table('campaigns', table => {
+        table.timestamp('start_at').nullable().defaultTo(null);
+    });
+
+    await knex('campaigns')
+        .whereIn('type', [CampaignType.REGULAR, CampaignType.RSS_ENTRY])
+        .whereIn('status', [CampaignStatus.SCHEDULED, CampaignStatus.SENDING, CampaignStatus.PAUSING, CampaignStatus.PAUSED])
+        .whereNotNull('scheduled')
+        .update({
+            start_at: knex.raw('scheduled')
+        });
+
+    await knex('campaigns')
+        .whereIn('type', [CampaignType.REGULAR, CampaignType.RSS_ENTRY])
+        .whereIn('status', [CampaignStatus.SCHEDULED, CampaignStatus.SENDING, CampaignStatus.PAUSING, CampaignStatus.PAUSED])
+        .whereNull('scheduled')
+        .update({
+            start_at: new Date()
+        });
+})();
+
+exports.down = (knex, Promise) => (async() => {
+})();
diff --git a/server/setup/knex/migrations/20190629170000_generalization_of_queued.js b/server/setup/knex/migrations/20190629170000_generalization_of_queued.js
new file mode 100644
index 00000000..ef8dee76
--- /dev/null
+++ b/server/setup/knex/migrations/20190629170000_generalization_of_queued.js
@@ -0,0 +1,25 @@
+exports.up = (knex, Promise) => (async() => {
+    const queued = await knex('queued');
+
+    for (const queuedEntry of queued) {
+        const data = JSON.parse(queuedEntry.data);
+
+        data.listId = queuedEntry.list;
+        data.subscriptionId = queuedEntry.subscription;
+
+        knex('queued')
+            .where('id', queuedEntry.id)
+            .update({
+                data: JSON.stringify(data)
+            });
+    }
+
+    await knex.schema.table('queued', table => {
+        table.dropColumn('list');
+        table.dropColumn('subscription');
+    });
+
+})();
+
+exports.down = (knex, Promise) => (async() => {
+})();