I don't think any of the common mail protocols are especially complex. If you're trying to do anything interesting with a mail client, it probably doesn't involve doing anything special with the protocols. Find a good library and tweak if you really need to.
I agree that everything he'll need can be found in a library but I believe that you always should get to know the internals of stuff, especially when it is as accessible and easy to learn as SMTP/POP/IMAP are.
That is half of what being a hacker means, striving to understand and tinker with the world&technology around us. It's why most of us took apart watches, radios & computers as young kids.
