[ramiss]

Basically POP3 will download all of the emails and remove them from the server. IMAP, on the other hand, will sync them. Which means they will be left on the server so you can also check them from another device/computer/browser etc.

IMAP also supports multiple folders and IMAP IDLE (similar to push email) and various other features. Whereas POP3 does not do any of this.