Quote Originally Posted by ArcaneMagus View Post
Is this related to Zimbra at all? Were you trying to access a Zimbra server? Are you using the Outlook connector? It sounds like you should be talking to your server's administrator...
My two cents to this... żbug?

We have the same problem with Zimbra 7.2.3. After some investigation we realized our nginx.http.web had TWO backend targets. However mailboxd was only installed in one of them.

Solution:
zmprov ms SERVER_WITH_NO_MAILBOXD zimbraReverseProxyLookupTarget FALSE
zmnginxctl restart