[Web] Adjust mailbox format

[Web] Include IMAP lib for future use
[Web] Fix default exception handler
[Web] Fix sync job edit forms
[Web] Other minor fixes

data/web/inc/vars.inc.php

@@ -142,3 +142,6 @@ $MAILBOX_DEFAULT_ATTRIBUTES['force_pw_update'] = false;
 
 // Force password change on next login (only allows login to mailcow UI)
 $MAILBOX_DEFAULT_ATTRIBUTES['sogo_access'] = true;
+
+// Default mailbox format, should not be changed, keep the trailing ":"
+$MAILBOX_DEFAULT_ATTRIBUTES['mailbox_format'] = 'mdbox:';