What is the difference between POP and IMAP?

What is the difference between POP and IMAP? I see both of them as an option in my email client, but what do they do?

Both the POP3 and IMAP protocol are methods that a client program can use to connect to an email server and check for mail, but the difference is in the method they use: POP3 connects just long enough to download a copy of the messages to the client, then (usually) deletes the messages from the server and logs off, whereas IMAP connects to the account and displays the messages on the server until you log off.

There's advantages and disadvantages to both: for one, POP3 connections take up less server bandwidth than IMAP.  The POP3 connection lasts long enough to download any new messages before logging off.  Whereas with IMAP, the connection remains until the email client is closed, or the mail server times out the connection. This is why most commercial ISPs only allow POP3 connections. Since messages downloaded via POP3 are downloaded to the client, they're always available on that computer, even if you're not connected to the Internet. However, if anything happens to your computer and those messages are deleted, there's nowhere else to retrieve them.

IMAP, on the other hand, has the advantage of the messages staying in one location: the server itself. This means that you can login to your account anywhere, with any IMAP client (or via webmail, like with WorldClient), and all your messages will be there. This also means that you don't have to worry about backing up your messages on your local machine; if something happens, simply reconfigure the account to connect to your account via IMAP, and they'll show up again. However, if you cannot access the Internet, you cannot get to your messages, unless your client saves a local copy of messages you read (such as Outlook or Outlook Express).

Additional Comments

Note that IMAP is only available in MDaemon Pro.

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