can't get NIS mail aliases to work

[Steven J. Backus]

  I'm new to the list and apologize if this has been covered.  I
recently changed from mail aliases in /etc/mail to the NIS aliases
map.  Now qpopper doesn't recognize them, saying "user unknown"
when anyone mails to an alias.  I'm on solaris 2.5.1 and I
downloaded the latest version of qpopper.  Is there a way to fix
this?

Thanks,
  Steve