rajat,I have already tried Incredimail.But then it was a bit heavy with too much of graphics. I just wanted to get a simple fast loading mail client .Another important thing was to get rid of MSN Messenger which loads along with Outlook Express.
There are two things mail clients and mail servers. Mail servers receive mails and distribute them in various accounts kept at the servers. Now whoever knows the password for a mail account can use a software installed in his machine (called mail client e.g. Outlook Express, Outlook, Incredimail, Ximian Evolution, KMail, Bat, Mozilla Mail, Courier, etc.) and retireve those mails from the server.
I hope I've been able to put it in simple enough terms to understand