Courier IMAP Services
You can manage these as part of init.d daemons
This is for user authentication, and is used by the pop3 and imap daemons.
Not secure, but might be easier for some users to setup. Also if their account is limited to reading mail only, it shouldn’t affect the whole system if their account is compromised.
As above but over ssl.
Not secure, but might be easier for some users to setup.