You can use webmail to see messages that have not been downloaded yet, and to post, but things can get hairy when a POP download happens while you are doing things.

It's not reccomended unless you are travelling, and have switched off the machine that would otherwise download messages.

This is part of why we do not recommend use of POP3, the other being that SPAM is pre-sorted for you into your SPAM folder, and that is not accessible with POP3