- Online and Offline mode
Although both protocols provide similar function - access to remote mail server in order to download email messages, IMAP is always better choice.
IMAP protocol is newer than POP3, and it offers many more functions and more optimal access to your remote mail account.
Most notable functions of IMAP protocol, that is not available in POP3, are:
If possible, always use IMAP protocol. Use POP3 only if your mail provider doesn't offer IMAP access to your account. For example, some web mail services may offer only POP3 access, as POP3 is simpler and easier to implement than IMAP.