IMAP vs. POP

What do they stand for?

IMAP

Internet Message Access Protocol

POP

Post Office Protocol

What's the difference?

The main difference, as far as we are concerned here, is the way in which IMAP or POP controls your e-mail inbox.
When you use IMAP you are accessing your inbox on the U of M's central mail server. IMAP does not actually move messages onto your computer. You can think of an e-mail program using IMAP as a window to your messages on the server. Although the messages appear on your computer while you work with them, they remain on the central mail server.
POP does the opposite. Instead of just showing you what is in your inbox on the U's mail server, it checks the server for new messages, downloads all the new messages in your inbox onto your computer, and then deletes them from the server. This means that every time you use POP to view your new messages, they are no longer on the central mail server. Figure 1 illustrates these concepts.

IMAP	POP
Figure 1: Accessing your inbox, IMAP versus POP.

IMAP makes it easier to view mail from home, work, and other locations

Because IMAP leaves all of your messages on the central mail server, you can view these messages from any location with Internet access. This means the U of M e-mail inbox you view from home will be the same one you see at work.
Since POP downloads new messages to your computer and removes them from the server, you will not be able to see those new messages on another computer when you check your inbox. Those messages exist only on the computer that downloaded them using POP.
However, if you use IMAP and create e-mail folders on the server, these folders are accessible from anywhere you read your e-mail using IMAP. If you use POP and create e-mail folders, they are stored locally, and you cannot access these folders from anywhere except the computer on which you created them.
POP can create problems if you alternate between it and IMAP. There is an option in many POP e-mail programs to leave copies of the messages on the server, but this option has complications. When you leave copies of the messages on the server, then access your e-mail using WebMail or another IMAP e-mail client, the POP client may create duplicate messages next time it accesses the inbox; you will see each of the messages more than once, and you will have to clean out (delete) the unwanted ones.

You may want to keep local copies

While using IMAP to save e-mail on the central mail server is recommended, there are reasons to have local copies of messages (messages downloaded to the computer, as with POP). Fortuanately, IMAP allows you to keep local copies of all your messages. The option of local copies is useful when you are connecting from a dial-up connection. You may want to download your messages, then disconnect from the Internet and work with your mail offline. Please note that while you are working offline, you cannot send or receive mail. You need to be connected to the Internet to do those tasks.

You have a backup of your e-mail with IMAP

The University's central e-mail servers are backed up every night. Thus, when your e-mail is stored on the U's e-mail server (as is the case with IMAP), a backup of your e-mail is made every night. These backups are used in the event of system failures or if a virus deletes your local mail. If you use POP, you lose your mail. The University cannot help you recover it because it was not stored the U's central e-mail server.
With the growing number of computer viruses and attacks from hackers, there is a greater possibility that e-mail can be deleted without your knowledge. The best insurance against loss of important e-mail is to have it on the University's e-mail server.