How can a desktop mail client be configured to read local mail?

This seems like something that should be doable, but I'm having no luck figuring it out and Google isn't helping much either.

Is there a way to use claws-mail (or another client) to view local mail (freebsd or linux) without the use of an smtp relay or anything?

It seems like I should be able to just point it to username@localhost or something and it would work, but I can't for the life of me figure out what I need to do.