I got duplicate logins to work for POP3, but not SMTP
I have duplicate user names (firstname.lastname@example.org, email@example.com), and I can log in with each via POP3 using the full email address as the user name. However, when I try to use authentiated SMTP (using Apple's Mail program in MacOSX 10.4.6) I can't authenticate. Nothing obvious in the logs, and nothing showed up in a search of the Zimbra forums. The Apple client authenticates to my CommuniGate Pro mail server without problems. I haven't tried other mail clients yet.