Hi there,
First of all welcome. It's always great to see more and more people taking to SME.
Secondly, not wishing to sound too cheeky but, might I suggest that you grab yourself a copy of the SME docs and have a read through. I think you'll find a lot of useful information in there about getting your server running and the various things that can be done using SME. You will also find an further details on configuring email.
In answer to your question, you sure can. I tend to use the IMAP protocol, no particular reason, just what I'm used to. When configuring the clients, just use the SME server IP for incoming and outgoing servers or you could of course specify you ISPs SMTP server for sending mail as I'm sure a fair few people do here.
Hope this helps,
Arthur