Disable mail from input if app manages it on its own

src/views/app.html

@@ -870,7 +870,7 @@
               <p ng-bind-html="'app.email.from.enableDescription' | tr:{ domain: app.domain, domainConfigLink: ('/#/email/' + app.domain) }"></p>
 
               <form role="form" name="emailForm" ng-submit="email.submit()" autocomplete="off">
-                <fieldset ng-disabled="!email.enableMailbox">
+                <fieldset ng-disabled="email.enableMailbox === '0'">
                   <div class="form-group" ng-class="{ 'has-error': emailForm.$dirty && email.error.mailboxName }">
                     <div ng-show="email.error.mailboxName">{{ email.error.mailboxName }}</div>