[Exim] User authentication

Hi

Is there any way exim4 can be configured to authenticate users (when
they check their e-mail) against the passwd file of a remote machine? I
need this because all my user accounts (12) are on another server which
is already serving http and samba. If a user wants to change password I
dont want to have to do it on two machines...

Is this even possible?
If not, there must be a similar way to achieve what I'm trying to do. I
read about LDAP and such but the complexity of such systems seems way
too big for a measle 12 users....

Thanks.
Jerome