Some Web sites, for e.g., Hotmail and Yahoo, provide e-mail service to anyone who wants it. They work as follows.
They have normal message transfer agents listening to port 25 for incoming SMTP connections. To contact, say, Hotmail, you have to acquire their DNS MX record, for e.g., by typing
Host –a –v hotmail.com
on a UNIX system. Suppose that the mail server is called mx10.hotmail.com, then by typing
telnet mx10.hotmail.com 25
you can establish a TCP connection over which SMTP commands can be sent in the usual way. So far, nothing unusual, except that these big servers are often busy, so it may take several attempts to get a TCP connection accepted.
The interesting part is how e-mail is delivered. Basically, when the user goes to the e-mail Web page, a from is presented in which the user is asked for a login name and password. When the user clicks on Sign In, the login name and password are sent to the server, which then validates them. If the login is successful, the server finds the user’s mailbox and builds a listing only formatted as a Web page in HTML. The Web page is then sent to the browser for display. Many of the items on the page are clickable, so messages can be read, deleted, and so on.
