[Exim] Q: Determine local user in localuser director?

Hi users,

I read in documentation about localuser director and there is written:

The localuser director checks whether the local part of an address is
the login of a local user, by calling the getpwnam() function.

man getpwnam says:

       getpwnam, getpwuid - get password file entry

       The  getpwnam()  function returns a pointer to a structure
       containing  the  broken  out  fields  of   a   line   from
       /etc/passwd for the entry that matches the user name name

My questions: Is possible to determine local user from database or
             through PAM? Is the solution to use aliasfile director with
             transport option (appendfile)?

Or behaviour of getpwnam() has changed in PAM system or in GLIBC 2.2 ?

Thanks for answers.

Bye Milan Kocian