[Dovecot] Why is dovecot involved in my smtp process

[Steve Campbell]

I've been trying to get smtp auth set up for days. All my sendmail and 
sasl2 stuff seems to be proper, but the user can't use the system on 
port 587, which is where I require authorization.

Now I see where messages are in my maillog of the type:

auth: pam_unix(dovecot:auth) : authentication failure ........

Why is dovecot involved in my smtp processes and how do I fix this. I've 
got some very mad users. The 10-auth.conf file is pretty much stock 
except for allowing plain text logins.

steve campbell