If you connect often to webmail or use a mail client with the Artifex, you should install the Artifex root SSL certificate so that you can avoid avoid “unrecognized SSL certificate” warnings, and to reduce the risk of a “man-in-the-middle” attack.
The URL for the certificate is:
http://artifex.org/_downloads/certs/cacert_2009-08-30.crt
Each OS has its own way for installing it, but chances are you can just download it and double click on it to install it.