imap problem on retrieving email
 

My remote server's imap program runs well, I can remotely telnet mail.my_domain.com 143 port and get positive response; now at my local machine I use a Mozilla as email client,
I set up the incoming server as mail.my_domain.com and 143 as port, when I try
to retrieve my email from my remote server, the system says: Login to server mail.my_domian.com failed, why?

Thx,
HTM