As we know e-mail clients are applications which enables us to read email offline from the desktop using POP/IMAP technologies.The main advantage in using e-mail client is that you can save it on your computer and print it conveniently but if your system crashes then you will lose all your saved mails.It is a matter of preference whether to use e-mail clients or not but it can be helpful when required.
Here is a addon for Firefox browser which is called as Simple Mail,the name itself suggest it is really simple and works great.It functions as an firefox addon which is compatible with firefox 3 and firefox 2.It integrates email client to your browser,by using Simple Mail you get notified, read and write email messages within the Firefox environment. You can configure one or more accounts in Preferences, set account refresh time and get notified of new mail.
As soon as you receive a fresh mail, Simple Mail shows the count in status bar. Also Simple Mail has a toolbar button, which you can put on a toolbar for easy access. You can click Simple Mail icon to open received messages in a separate browser tab. The search function which is on the top right helps a lot in searching your emails faster and easier.If you are looking to set up a e-mail client then I suggest you to go with Simple help which is quite helpful and small in terms of size!
Install Simple mail version 2.68 (size 170 Kb)

I never really bother with email clients, I just use gmail
well in this area i think thunderbird is the best. moreover you can leave a copy of your messages on the server so even if your system crashes you won’t loose any data!
Simple mail is used in my school. Haven’t tried it though…