Stands for "Internet Message Access Protocol" and is pronounced "eye-map." It is a method of accessing e-mail messages on a server without having to download them to your local hard drive. This is the main difference between IMAP and another popular e-mail protocol called "POP3."
POP3 requires users to download messages to their hard drive before reading them. The advantage of using an IMAP mail server is that users can check their mail from multiple computers and always see the same messages. This is because the messages stay on the server until the user chooses to download them to his or her local drive. Most webmail systems are IMAP based, which allows people to access to both their sent and received messages no matter what computer they use to check their mail.
Most e-mail client programs such as Microsoft Outlook and Mac OS X Mail allow you to specify what kind of protocol your mail server uses. If you use your ISP's mail service, you should check with them to find out if their mail server uses IMAP or POP3 mail. If you enter the wrong protocol setting, your e-mail program will not be able to send or receive mail.