how to use non-default username/password file

[Anthony]

I need to use a non-default username/password file to allow users to pop
in to our mail server. I kow by default that popper uses the /etc/passwd
file to authenticate users for pop login. How do you specify a different
file (ndmb format) in place of the /etc/passwd file. I did read the
install documentation but it does not tell you how to do this. Can it be
done?

Any help would be greatly appreciated!

Thanks,
  Anthony