It is becoming more and more common to access email via a web-based (HTTP) interface. This way, there is no need to use any specific email client on any specific machine. Any browser on any computer can now read email messages.
Web-based email still requires an SMTP server to receive messages, and it also needs to use the same standard to store and organize messages as the selected SMTP server (mbox or Maildir). Some webmail engines, such as Squirrelmail, uses the IMAP interface to access email, which makes it even more flexible.
There are many web-based email access interfaces. The most well known one is Squirrelmail (http://www.squirrelmail.org/), but there are others, such as Openwebmail (http://www.openwebmail.org/).