[Dovecot] Certificate Server name!

Setup of Dovecot went smoothly.

Now when I try to retrieve mail from the server, I get the following message:

Security Error: Domain name mismatch

You have attempted to establish a connection to "mail.tib.com" However, the security certificate presented belongs to "imap.tib.com".....

How to fix this message?

Thanks in advance.

Kirt