Are you working with POP3/IMAP/SMTP accounts? The reason that I ask is that
one of them is most likely marked to do SSL. So if you are using Outlook
2002/2003, try selecting Tools > Email Accounts > View/Change existing
accounts > Highlight an account > Change button > More options and then the
last tab if my memory serves me right.
Note: If your ISP requires SSL connectivity to send/receive mail, you need
to get a copy of that certificate installed on your machine. The ISP should
be able to provide a copy of it so you can install it. (just have to double
click on the *.cer file and a wizard will popup to guide you the rest of the
way.