I have normal system users, some and some virtual domains (2 different flavors).

I have this job that runs from cron on my own userid to archive mail

I want Dovecot to use my system password for mail authentication.

I, therefore, use PAM to authenticate system users

Everything works great, modulo getting the auto-index to be visible using RoundCube (which if I log into roundcube using <user>@<domain> it does). 

by default if I'm logged in as my normal OS user, default doveadm commands (as issued from the shell or from my archive script) use the user I'm logged in as *WITHOUT A DOMAIN*.

I want to default PAM auth'd users to append @lerctr.org (DOMAIN) to the OS user.

when they log in to roundcube as the OS user, right?

John