diff --git a/src/views/apps.html b/src/views/apps.html
index 6bc5f5adf..b106e0b3e 100644
--- a/src/views/apps.html
+++ b/src/views/apps.html
@@ -112,24 +112,26 @@
                                 </div>
 
                                 <div class="form-group" ng-show="appConfigure.app.manifest.addons.sendmail" ng-class="{ 'has-error': !appConfigureForm.mailboxName.$dirty && appConfigure.error.mailboxName }">
-                                    <label class="control-label">Mailbox Name</label>
-                                    <div class="control-label" ng-show="appConfigure.error.mailboxName">{{appConfigure.error.mailboxName}}</div>
+                                    <input type="checkbox" id="appConfigureMailboxNameEnabled" ng-model="appConfigure.mailboxNameEnabled">
+                                    <label class="control-label" for="appConfigureMailboxNameEnabled">Custom Mailbox Name</label>
+                                    <div class="has-error" ng-show="appConfigure.error.mailboxName">{{ appConfigure.error.mailboxName }}</div>
 
                                     <div class="input-group form-inline">
-                                        <input type="text" class="form-control" id="appConfigureMailboxNameInput" name="mailboxName" ng-model="appConfigure.mailboxName" uib-tooltip="App FROM email address">
+                                        <input type="text" class="form-control" id="appConfigureMailboxNameInput" ng-required="appConfigure.mailboxNameEnabled" name="mailboxName" ng-model="appConfigure.mailboxName" uib-tooltip="App FROM email address. Addresses ending with '.app' are reserved." ng-disabled="!appConfigure.mailboxNameEnabled">
 
                                         <div class="input-group-btn">
-                                            <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">
+                                            <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" ng-disabled="!appConfigure.mailboxNameEnabled">
                                                 @{{ appConfigure.domain.domain }}
                                             </button>
                                         </div>
                                     </div>
                                 </div>
 
-                                <div class="has-error" ng-show="appConfigure.error.alternateDomains">{{ appConfigure.error.alternateDomains }}</div>
                                 <div class="form-group" ng-class="{ 'has-error': (appConfigureForm.alternateSubdomain.$dirty && appConfigureForm.alternateSubdomain.$invalid) || (!appConfigureForm.alternateSubdomain.$dirty && appConfigure.error.alternateDomains)  }">
                                   <input type="checkbox" id="appConfigureAlternateDomainEnabled" ng-model="appConfigure.alternateDomainEnabled">
                                   <label class="control-label" for="appConfigureAlternateDomainEnabled">Redirect the following domain to this app</label>
+                                  <div class="has-error" ng-show="appConfigure.error.alternateDomains">{{ appConfigure.error.alternateDomains }}</div>
+
                                   <div class="input-group form-inline">
                                     <input type="text" class="form-control" ng-model="appConfigure.alternateSubdomain" id="appConfigureAlternateSubdomainInput" name="alternateSubdomain" placeholder="Leave empty to use bare domain" ng-disabled="!appConfigure.alternateDomainEnabled">
 
diff --git a/src/views/apps.js b/src/views/apps.js
index 1915d9ff3..254131a34 100644
--- a/src/views/apps.js
+++ b/src/views/apps.js
@@ -36,6 +36,7 @@ angular.module('Application').controller('AppsController', ['$scope', '$location
         accessRestriction: { users: [], groups: [] },
         xFrameOptions: '',
         alternateDomainEnabled: false,
+        mailboxNameEnabled: false,
         alternateSubdomain: '',
         alternateDomain: null,
         ssoAuth: false,
@@ -64,6 +65,7 @@ angular.module('Application').controller('AppsController', ['$scope', '$location
             $scope.appConfigure.alternateDomain = app.alternateDomains[0] ? $scope.domains.filter(function (d) { return d.domain === app.alternateDomains[0].domain; })[0] : $scope.appConfigure.domain;
             $scope.appConfigure.robotsTxt = app.robotsTxt;
             $scope.appConfigure.enableBackup = app.enableBackup;
+            $scope.appConfigure.mailboxNameEnabled = app.mailboxName && (app.mailboxName.match(/\.app$/) === null);
             $scope.appConfigure.mailboxName = app.mailboxName || '';
 
             $scope.appConfigure.ssoAuth = (app.manifest.addons['ldap'] || app.manifest.addons['oauth']) && app.sso;
@@ -146,13 +148,17 @@ angular.module('Application').controller('AppsController', ['$scope', '$location
             // The backend supports multiple alternateDomains, however we only have ui for one
             if ($scope.appConfigure.alternateDomainEnabled) data.alternateDomains = [{ domain: $scope.appConfigure.alternateDomain.domain, subdomain: $scope.appConfigure.alternateSubdomain }];
 
-            if ($scope.appConfigure.mailboxName !== $scope.appConfigure.app.mailboxName) data.mailboxName = $scope.appConfigure.mailboxName;
+            if ($scope.appConfigure.mailboxNameEnabled) {
+                data.mailboxName = $scope.appConfigure.mailboxName;
+            } else { // setting to empty will reset to .app name
+                data.mailboxName = '';
+            }
 
             Client.configureApp($scope.appConfigure.app.id, data, function (error) {
                 if (error) {
                     if (error.statusCode === 409 && (error.message.indexOf('is reserved') !== -1 || error.message.indexOf('is already in use') !== -1)) {
                         $scope.appConfigure.error.port = error.message;
-                    } else if (error.statusCode === 409 && error.message.indexOf('mailbox') !== -1 ) {
+                    } else if (error.statusCode === 400 && error.message.indexOf('mailbox') !== -1 ) {
                         $scope.appConfigure.error.mailboxName = error.message;
                         $scope.appConfigureForm.mailboxName.$setPristine();
                         $('#appConfigureMailboxNameInput').focus();