file/folder perms permissions

Forgive me if I am blind, but I cannot find default folder permissions.

For the home directories, with the sub of mail: and deeper, I see some files with 660, some with 600, some folders with 770 some with 660

I am a bit confused. I manually messed with some files, and my MUA complained about permissions. So I got that mess fixed, and in doing so I noticed the seemingly contradictory permissions.

Thanks!