Rice webmail page http://webmail.rice.edu is not a purely web-based mail system like yahoo mail or hotmail, it provides another way to access your emails on your Unix accounts. If you are away on vacation or conference, and there is no remote access software like SSH available, webmail might be your only choice. You only need to go to the Rice Webmail Page http://webmail.rice.edu, select your mail server and then log in with your appropriate Unix user name and password (most of us use stat.rice.edu). All other operations are straightforward.
If you will be away for a relatively long period of time and would like to keep reliable email connection with others, prepare yourself with an alternate method. Forwarding all your email to your real web account such as yahoo might be a good idea since yahoo is more reliable and accessible than Rice webmail. Procmail can do this for you.