Looks like the Application ignores all parts after the @ in the login-name.
I can't login to my server because I use the full E-Mail as login.
My Mail-Log says that it just auth with the first part:
Jun 21 10:21:41 cghostgroup smtp_auth: smtp_auth: FAILED: mymailaddy - password incorrect from (null)@(null) [195.95.176.193]