What is the difference between using POP3 and IMAP?

IMAP keeps in sync with your inbox. POP3 will just download the messages into Outlook. marking it read with pop3 will not mark it read in your "real" inbox (in other words only marking read ur local copy) in imap, when u mark as read, in outlook, "ur real inbox"'s messages get marked as read or erased.. wat ever you do. understand?

Without going into deep detail. POP3 and IMAP are two protocols for accessing a webserver. Here is the best way to see how it works. If a mail server (from here on out called Mail Man Bob) has some mail for you, you can retrieve this mail from him in one of multiple ways. The two we will talk about are POP3 and IMAP If you are using POP3 when you ask Mail Man Bob for your mail he will give you copies of it to store on your local machine and keep a copy for himself, unless you tell him to delete his copies after giving you a copy. This allows you to download mail to say your phone but still keep a copy around in case you want it off of your phone or you just want to keep a spare copy around. If you're using IMAP when you ask Mail Man Bob for your mail he will tell you "Ok I have these messages which are unread, read, deleted, and in these folders" You can then ask him for copies of these messages, mark messages as read, delete them or move them. The primary difference is that with POP3 you're pulling the mail to your local machine to work with, while with IMAP you are doing everything on the server. The secondary difference is that IMAP has 'Push' capabilities. That is an IMAP server can send updates to you without you having to poll the server for updates. I hope that answers your questions.

The big difference from the user's viewpoint is that if you use more than one computer, with POP3, if you read an email in one computer, it won't be there if you look with the other computer, unless you always leave email on the server with the first program and don't with the second. With IMAP, you can have any number of computers connected to the email server and they'll all get all the email.