Question : POP3 Vs IMAP

Regarding about POP3 and IMAP4, it looks like they both can download a copy of the message from the serverand leave the original copy at the server.
So what is the difference between POP3 and IMAP?
Thanks

Answer : POP3 Vs IMAP

This should give you a good run-down:

http://en.wikipedia.org/wiki/Pop3

http://en.wikipedia.org/wiki/Imap