Webmail (or Web-based e-mail) is an e-mail service intended to be primarily accessed via a web browser, as opposed to through a desktop e-mail client (such as Microsoft Outlook, Pegasus Mail, Mozilla's Thunderbird, or Apple Inc.'s Mail). Very popular webmail providers include Gmail, Yahoo! Mail, Hotmail, and AOL.
One advantage of webmail over application-based e-mail is that a user has the ability to access their inbox from any Internet-connected computer around the world. However, the need for Internet access is also a drawback, in that one cannot access old messages when not connected to the Internet (with the exception of some newer technologies, such as Gmail's "Offline Mail" feature). On the other hand, if one uses the IMAP protocol through an application-based e-mail client, all contents of the mailbox will be consistently displayed in both the webmail and the PC e-mail client contexts.
The first webmail software was called simply WebMail and was developed in perl by Luca Manunzawhen he was working at CRS4, in Sardinia. The first working demo was released on March 10, 1995; thereafter the source was released (with registration required) on March 30, 1995.
There are also software packages that allow organizations to offer e-mail through the web for their associates. Some solutions are open source software like SquirrelMail, RoundCube, BlueMamba, IlohaMail, and UebiMiau, while others are closed source like the Outlook Web Access module for Microsoft Exchange. Conversely, there are programs that can simulate a web browser to access webmail as if it were stored in a POP3 or IMAP account. They are susceptible, though, to changes in the user interface of the web service since there is no standard interface.
Some providers offer web access to other's e-mail servers. This allows web access to mailboxes where the mail server does not offer a web interface, or where an alternative interface is desired.