X-based mail clients are more easy-to-use, with the cost that they are in general much bigger (than text-based mail clients_ and thus need more time to load. Another disadvantage is that you can not start them remotely without an X-server (for example, X-Win32) and you do need at least DSL/Cable Modem connection to start them via SSH+X-Win32 in a reasonable amount of time.
If you are using CDE (Common Desktop Environment), dtmail is the default mailer. It lacks many important features of modern mail clients and is very slow when you have a big mailbox. However, it provides a decent interface to basic emailing jobs and can be used if you need a light-weight X-based mailer. dtmail can be started from command line or by clicking the mail icon of your CDE panel. You need to add /usr/dt/bin to your $PATH to start dtmail from command line.
Netscape messenger is a much more sophisticated X-based mail client than dtmail, comparable to OE under windows. It supports HTML email, multiple POP3, IMAP accounts, encryption, MIME, provides incoming filter, ability to import emails from other mail clients, full-featured address book.
To start Netscape messenger, open Netscape and choose messenger from communicator menu or click the messenger icon at the lower-right corner of any browser window. You can also let Netscape open messenger automatically if you set starting options from Edit -> Preference -> Appearance. Other options, including accounts can be set at the mail and newsgroups section of the preference window.
Mozilla is a GNU licensed broswer based on Netscape. Its messenger is more robust than Netscape messenger and has quite a few new features. You can start mozilla by typing
/usr/site/mozilla/bin/mozillaor add /usr/site/mozilla/bin to your $PATH. Mozilla messenger can be brought up in the same way as netscape messenger.