I have access to both IMAP and POP3 email accounts. For the life of me, I fail to see the difference between the two protocols. Can you explain the essential differences?

Of the two protocols, IMAP (which stands for Internet Message Access Protocol) is newer than POP (which stands for Post Office Protocol) and is more flexible and efficient. POP essentially requires the client to manage the mailbox, whereas IMAP enables the server to manage the mailbox.

IMAP is useful in an offline situation and is particularly advantageous when your client machines are powerful but your servers aren't or when your clients connect to your email server through expensive dial-up connections. IMAP has the potential for online performance optimization, which can offer good performance over slow connections. Furthermore, you can download sections of a message, rather than the entire message, from an IMAP server. Although not usually enabled, these IMAP capabilities provide a true advantage. IMAP also has the advantage of being able to access non-email data (e.g., NetNews, documents). IMAP can manage multiple mailboxes on the same or different servers. Likewise, numerous users can access shared mailboxes.

More applications are available to work with POP than with IMAP, however. POP's maturity probably plays a role in its broader use.