1) POP (Post Office Protocol):

It is very simple email protocol. When the POP e-mail server receives an e-mail it stores that e-mail on the server and waits for you to request it.

When you open mail program (e.g., Outlook) and hit the Send/Receive button request for the email is sent to the server. When the Send/Receive button is pressed, e-mail program asks to the server “if any mail there on the server? If yes, send it to me.”

When the POP server receives this request from your e-mail program it sends the entire message to your e-mail program. Once the POP server has sent the e-mail to your e-mail program it does not have the message on the server anymore unless you specifically tell it to keep a copy. POP is basically a flow through entity—it just passes on the information to you at your e-mail program. This is different from IMAP which is interactive with your e-mail program.

2) IMAP (Internet Message Access Protocol):

IMAP allows you to download e-mails from the server to your e-mail program on your computer the same as POP. However, what IMAP does differently than POP is that when you request your e-mail from the server it sends you a copy from the server rather than sending you the entire e-mail.

IMAP keeps a copy of the e-mail on the server while you have a copy on your computer.  In case if certain messages on local computer and IMAP has different messages on the IMAP mail server then when you connect with the IMAP mail server with your local computer IMAP senses that there are differences between the two and synchronize them so that they have the same information.

For example, if you have deleted some messages and are composing some more and have sent some others this information will be synced up with the IMAP server so the IMAP server will delete the copies of the messages you deleted. It makes it so by the time you log off with the IMAP server you have two complete copies of all of your e-mail functions: one on the IMAP server and one on your local computer.

(Posted By Nia on Tuesday, July 04, 2006)