What is POP?
POP is short for Post Office Protocol. POP is one method used by e-mail programs to retrieve e-mail from the server. The important feature of POP is that when you retrieve your mail the messages are moved from the server to the computer you use to check mail.

What is IMAP?
IMAP is short for Internet Message Access Protocol. It is the other main method used by e-mail programs to retrieve mail. Unlike POP, IMAP keeps your messages on the server. When you click to read a message IMAP presents the message that is stored on the server.

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  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 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.

IMAP

IMAP is a great choice for users who wish to check their mail from different computers.

If you have ever used webmail before, then you’ve already used IMAP. When you log into the IMAP server with your password, you are seeing your messages and folders as they exist on the server, regardless of which computer you are using.

One thing to remember is that disk space is limited on the server. Your email quota is 1 GB, so eventually storage might become an issue. It is good practice to periodically clean up any unwanted messages. However, if you are using a program like Outlook or Thunderbird, you have the option to save messages to local folders (on your machine).

POP

POP is suitable if you are going to use e-mail only from one location, such as your home or office, because all your e-mail activities are performed on your local workstation.

Mail is “popped” (downloaded) from the inbox of the email server to your local machine, either manually or according to a preset time interval. The email is stored on your local computer where you can create folders that may or may not match the folders you might have on the email server.

Since the e-mail is normally deleted from the server when it is downloaded, you are responsible for making backup copies. Also, your downloaded e-mail will not be on the server if you attempt to access it from a different computer. Although you can choose a POP setting to “leave mail on the server”, you cannot use folders, filters, or any other client capabilities on the server, and leaving e-mail on the server can result in your exceeding your allowable disk space.

Which should I use, POP or IMAP?

Our experience shows that how users interact with their e-mail is intensely personal, and the decision is ultimately yours. However, here are some general guidelines:

• Use POP or IMAP; do not mix the two. Doing so will cause all sorts of problems.
• Use POP if you read your mail on only one computer.
• If you use more than one computer to read e-mail use IMAP.
• If you need to use more than one e-mail program to read your mail, set each program to use IMAP.
• Do you use Alphamail occasionally, in addition to an e-mail program? Use IMAP. (Alphamail is an IMAP-only e-mail client.)
• Some e-mail programs have a “leave mail on server” option that simulates IMAP mode. If you use this feature please consider using IMAP.