SMTP / IMAP / POP Banner Troubleshooting
Since SMTP, POP3 and IMAP4 all send a banner message before the client begins a request, Server Initiating Protocols must be set if the service operates at Layer 7. Please make sure this is set to the proper value.
If this is not set, it can cause the service to appear up and respond to pings and telnet, but the application will not work. A good way to test this is by telnet to the service: if the connection succeeds but does not display a banner message, this is the likely culprit.