diff --git a/migrations/20190303024631-apps-default-mailboxName.js b/migrations/20190303024631-apps-default-mailboxName.js
new file mode 100644
index 000000000..a63b4570e
--- /dev/null
+++ b/migrations/20190303024631-apps-default-mailboxName.js
@@ -0,0 +1,27 @@
+'use strict';
+
+var async = require('async'),
+    crypto = require('crypto'),
+    fs = require('fs'),
+    os = require('os'),
+    path = require('path'),
+    safe = require('safetydance'),
+    tldjs = require('tldjs');
+
+exports.up = function(db, callback) {
+    db.all('SELECT * FROM apps, subdomains WHERE apps.id=subdomains.appId AND type="primary"', function (error, apps) {
+        if (error) return callback(error);
+
+        async.eachSeries(apps, function (app, iteratorDone) {
+            if (app.mailboxName) return iteratorDone();
+
+            const mailboxName = (app.subdomain ? app.subdomain : JSON.parse(app.manifestJson).title.toLowerCase().replace(/[^a-zA-Z0-9]/g, '')) + '.app';
+
+            db.runSql('UPDATE apps SET mailboxName=? WHERE id=?', [ mailboxName, app.id ], iteratorDone);
+        }, callback);
+    });
+};
+
+exports.down = function(db, callback) {
+    callback();
+};
diff --git a/migrations/schema.sql b/migrations/schema.sql
index da0c2341f..175f73543 100644
--- a/migrations/schema.sql
+++ b/migrations/schema.sql
@@ -83,7 +83,7 @@ CREATE TABLE IF NOT EXISTS apps(
     robotsTxt TEXT,
     enableBackup BOOLEAN DEFAULT 1, // misnomer: controls automatic daily backups
     enableAutomaticUpdate BOOLEAN DEFAULT 1,
-    mailboxName VARCHAR(128), // mailbox of this app
+    mailboxName VARCHAR(128), // mailbox of this app. default allocated as '.app'
 
     // the following fields do not belong here, they can be removed when we use a queue for apptask
     restoreConfigJson VARCHAR(256), // used to pass backupId to restore from to apptask
diff --git a/src/appdb.js b/src/appdb.js
index e4e389d84..bbd13d976 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -265,6 +265,7 @@ function add(id, appStoreId, manifest, location, domain, ownerId, portBindings,
     assert.strictEqual(typeof ownerId, 'string');
     assert.strictEqual(typeof portBindings, 'object');
     assert(data && typeof data === 'object');
+    assert(typeof data.mailboxName === 'string' && data.mailboxName); // non-empty string
     assert.strictEqual(typeof callback, 'function');
 
     portBindings = portBindings || { };
@@ -281,7 +282,7 @@ function add(id, appStoreId, manifest, location, domain, ownerId, portBindings,
     var robotsTxt = 'robotsTxt' in data ? data.robotsTxt : null;
     var debugModeJson = data.debugMode ? JSON.stringify(data.debugMode) : null;
     var env = data.env || {};
-    const mailboxName = data.mailboxName || null;
+    const mailboxName = data.mailboxName;
 
     var queries = [];