[Dovecot] Dovecot configuration with passwd-file

[Spectron International, Inc.]

I have tried to configure dovecot to use passwd-file authentication and I
havent been able to. I changed the following in the dovecot.conf file (I
want to have all the mailboxes in one directory):

default_mail_env = maildir:/opt/mail/%u
auth_userdb = passwd-file /etc/passwd.imap
auth_passdb = passwd-file /etc/passwd.imap
auth_verbose = yes

It gives me the following error (I hoped it would be more verbose than
this):

Internal login failure: f_rojas [192.168.10.4].

passwd.imap exists, the user and password are ok What am I missing?

Fawzib Rojas