diff --git a/src/appdb.js b/src/appdb.js
index b9cf71b47..7588d7d73 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -60,7 +60,7 @@ var assert = require('assert'),
 
 var APPS_FIELDS_PREFIXED = [ 'apps.id', 'apps.appStoreId', 'apps.installationState', 'apps.installationProgress', 'apps.runState',
     'apps.health', 'apps.containerId', 'apps.manifestJson', 'apps.httpPort', 'apps.location', 'apps.domain', 'apps.dnsRecordId',
-    'apps.accessRestrictionJson', 'apps.restoreConfigJson', 'apps.oldConfigJson', 'apps.updateConfigJson', 'apps.memoryLimit', 
+    'apps.accessRestrictionJson', 'apps.restoreConfigJson', 'apps.oldConfigJson', 'apps.updateConfigJson', 'apps.memoryLimit',
     'apps.altDomain', 'apps.xFrameOptions', 'apps.sso', 'apps.debugModeJson', 'apps.robotsTxt', 'apps.enableBackup',
     'apps.creationTime', 'apps.updateTime' ].join(',');
 
@@ -226,6 +226,7 @@ function add(id, appStoreId, manifest, location, domain, portBindings, data, cal
 
     database.transaction(queries, function (error) {
         if (error && error.code === 'ER_DUP_ENTRY') return callback(new DatabaseError(DatabaseError.ALREADY_EXISTS, error.message));
+        if (error && error.code === 'ER_NO_REFERENCED_ROW_2') return callback(new DatabaseError(DatabaseError.NOT_FOUND, 'no such domain'));
         if (error) return callback(new DatabaseError(DatabaseError.INTERNAL_ERROR, error));
 
         callback(null);
diff --git a/src/maildb.js b/src/maildb.js
index 8f2b63c4b..103fb991f 100644
--- a/src/maildb.js
+++ b/src/maildb.js
@@ -38,6 +38,7 @@ function add(domain, callback) {
 
     database.query('INSERT INTO maildb (domain) VALUES (?)', [ domain ], function (error) {
         if (error && error.code === 'ER_DUP_ENTRY') return callback(new DatabaseError(DatabaseError.ALREADY_EXISTS, 'mail domain already exists'));
+        if (error && error.code === 'ER_NO_REFERENCED_ROW_2') return callback(new DatabaseError(DatabaseError.NOT_FOUND), 'no such domain');
         if (error) return callback(new DatabaseError(DatabaseError.INTERNAL_ERROR, error));
 
         callback(null);
diff --git a/src/test/database-test.js b/src/test/database-test.js
index 6ab6b0600..f4170166b 100644
--- a/src/test/database-test.js
+++ b/src/test/database-test.js
@@ -19,6 +19,7 @@ var appdb = require('../appdb.js'),
     groupdb = require('../groupdb.js'),
     hat = require('hat'),
     mailboxdb = require('../mailboxdb.js'),
+    maildb = require('../maildb.js'),
     settingsdb = require('../settingsdb.js'),
     tokendb = require('../tokendb.js'),
     userdb = require('../userdb.js'),
@@ -1735,4 +1736,55 @@ describe('database', function () {
             });
         });
     });
+
+    describe('mail', function () {
+        const DOMAIN_0 = {
+            domain: 'foobar.com',
+            zoneName: 'foobar.com',
+            provider: 'digitalocean',
+            config: { token: 'abcd' }
+        };
+
+        const MAIL_DOMAIN_0 = {
+            domain: DOMAIN_0.domain,
+            enabled: false,
+            relay: { provider: 'cloudron-smtp' },
+            catchAll: [ ],
+            mailFromValidation: true
+        };
+
+        before(function (done) {
+            domaindb.add(DOMAIN_0.domain, { zoneName: DOMAIN_0.zoneName, provider: DOMAIN_0.provider, config: DOMAIN_0.config }, done);
+        });
+
+        it('can add mail domain', function (done) {
+            maildb.add(MAIL_DOMAIN_0.domain, done);
+        });
+
+        it('cannot add same domain twice', function (done) {
+            maildb.add(MAIL_DOMAIN_0.domain, function (error) {
+                expect(error).to.be.ok();
+                expect(error.reason).to.be(DatabaseError.ALREADY_EXISTS);
+                done();
+            });
+        });
+
+        it('cannot add non-existing domain', function (done) {
+            maildb.add(MAIL_DOMAIN_0.domain + 'nope', function (error) {
+                expect(error).to.be.ok();
+                expect(error.reason).to.be(DatabaseError.NOT_FOUND);
+                done();
+            });
+        });
+
+        it('can get domain', function (done) {
+            maildb.get(MAIL_DOMAIN_0.domain, function (error, result) {
+                expect(error).to.equal(null);
+                expect(result).to.be.an('object');
+                expect(result).to.eql(MAIL_DOMAIN_0);
+
+                done();
+            });
+        });
+    });
 });