[Dovecot] Mapping usernames

[Henry]

Greets,

We're using Dovecot 1.0.7 (which comes with CentOS 5.x).

I have successfully configured dovecot to change a username from abc at 123.com to realname1_abc for a machine which only has a single domain (using auth_username_format=realname1_%Ln).

However, I'm pulling my hair out trying to get dovecot to handle multiple domains (the machine has existing /etc/passwd /etc/shadow and /etc/mail/virtusertable users).  On an older machine, I simply hacked the source code to perform a berkeley DB lookup in /etc/mail/virtusertable.db for the realname[a-z0-9]_xx.  This time round, though, I'm trying to do this cleanly.

I've been reading the docs/wiki/etc but I now can't see the forest for the trees.  This is what I've got so far:

In /etc/dovecot.conf:
...
auth default {

    userdb passwd-file {
        args = /etc/dovecot.passwd
    }

    passdb passwd-file {
        args = /etc/shadow
        #args = /etc/dovecot.passwd
    }
}

/etc/dovecot.passwd contains:
realnamea_abc:{PLAIN-MD5}$1$Vjkfhaa....::::::userdb_user=abc at 123.com

I've been fiddling around blindly with all kinds of settings in userdb {} above, but I always get the error:
"passwd-file(abc at 123.com,::ffff:127.0.0.1): unknown user", amongst others.

In a nutshell, I want to allow a user to login with abc at 123.com, this name must be mapped to a real system user (eg, using /etc/dovecot.passwd), then authenticated against /etc/shadow or the MD5 password in /etc/dovecot.passwd

I would appreciate any kind of pointers or advise here.  It would have been nice if vpopmail allowed me to call an external perl script where I could perform the username mapping, but alas, this is not possible.

Thanks
Henry

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