Compare and contrast three different internet protocols commonly used to retrieve mail from mail servers by email user agents?

Answer 1

There are only two standard protocols used to retrieve electronic mail from mail servers by email user agents: Post Office Protocol (POP) and internet Message Access Protocol (IMAP).

POP is designed to be a very simple protocol for downloading new mail. It is suitable for use when a user wants to store all of his mail on his own personal computer. Mail is downloaded by the user agent from a POP server to the user's computer. Once successfully downloaded, the user agent (in normal operation) will delete the messages that have been downloaded. (Many user agents support a "Leave mail on server" option, but in general POP does not work as well as IMAP for the case where a user wants to access his email from different computers.)

By contrast to POP, IMAP was designed for the case where a user's mail is maintained on a server and accessed by one or more computers. To this end, IMAP supports many more features than POP, including: the ability to search messages, support for multiple mail folders, and support for downloading attachments separately from the messages themselves.

Most user agents support both POP and IMAP. However, many service providers support only POP, or charge extra to provide IMAP support.

Strictly speaking, "webmail" is not a protocol used to retrieve mail from a mail server by a mail user agent. However, webmail is widely used as a means to allow users to remotely access their electronic mail. Essentially, webmail is an implementation of a mail user agent on a web server. The user then uses an ordinary web browser, rather than a mail user agent, to access his mail. Often the webmail server uses IMAP to access the messages from the server where the mail is actually stored.