Postfix: The Definitive Guide

POP and IMAP

After Postfix has delivered a message, users need a way to read it. Many sites provide a POP/IMAP server for users to retrieve their email messages over the network. In most cases Postfix works seamlessly with POP/IMAP servers, so that no special configuration is required on either side.

POP Versus IMAP

The POP protocol works best when you have limited, or less than full-time, network access because it allows you to connect to your mail server, fetch all of your messages, and disconnect from the network. You now have local copies that you can read offline. Most POP clients have a configuration option to delete your messages from the server when you retrieve them, since you then have the local copies. If you don’t delete them at some time, the messages accumulate, taking up more and more space on your mail server. POP was designed to be easy to implement, but the major problem with the POP protocol is that if you ever work from more than one computer, your messages may not be where you need them. It also does not handle multiple mailboxes very well, and it forces you to download complete messages. There is no option to retrieve just the subject, for example, to decide if you want the complete message.

The IMAP protocol was designed to overcome some of POP’s shortcomings. It keeps all messages on the server. You have to be connected while working with your email messages, but you can manage them as if they were local. Since everything happens on the server, it doesn’t matter ...