Demystifying email protocols: Crabby's Daily Tip

There are about six most commonly used protocols; here are three of them. For more in-depth info about these and about the others visit this article, and look under the heading Email account types.

1. POP3   When you use the very common Post Office Protocol 3 (POP3), your email is stored on your email provider's server initially. But once you go and "get it" from Outlook (or whatever e-mail program you use), it's downloaded to your computer and is no longer stored on the server. If you want to keep it, you have two choices: never delete it from your program, or create a copy of it and keep it somewhere on your computer.
   
   Use POP3 when:
   • You have one computer and want to store all your mail on that computer.
   • Security is a concern — you don't want your messages stored on an external server.
   • You don't want to have to be connected to the Internet to be able to read email.
2. IMAP   Internet Message Access Protocol (IMAP) is a way to access your email on a server and, if you like, keep your email messages stored there instead of on your local computer. An example of a service that uses IMAP mail is Gmail.
   
   Use IMAP when:
   • You have multiple computers and you want to be able to access your email from any one of them (and the Web).
   • You want to create and move folders or mailboxes, delete messages, and even perform a search for certain parts of a message — all on the server.
   • You want to view just the headers of your email messages and decide whether you want to download them. No need to download an entire spam message when the heading is shocking enough.
3. MAPI    MAPI is a lot like IMAP (in fact, it's an anagram of it), but it provides a wider array of features when you use it from within Outlook. In fact, MAPI makes it possible for other Office programs (such as Word, Excel, and OneNote) to work with your email program.
   
   Use MAPI when:
   • You want to use profiles to configure how a message is transmitted and where it is stored.
   • You need your email program (such as Outlook) to work with another program (such as Word).
   • Your organization uses Outlook with Exchange Sever so you have no choice in the matter.

 Again, to learn more about email protocols, take a look at this article, and read the content under Email account types. 

— Crabby 

More info on Outlook IMAP:

Better IMAP in Outlook 2010