I've been trying to collect mail from Zimbra using a pop3 client. I keep getting an error message: sending of username did not succeed. Mail pop3.blabla.com responded: only valid after entering TLS mode.

I've tried changing each of the POP3 settings on the server but can't clear the error.

I can turn on SSL on the client and get a successful login. But, I have users out there that won't know to do that when we convert to this server.

Is there a postfix config option I need to manually add?