[Dovecot] Virtual servers

Hello

I'm migrating from Courier to Dovecot (1.0.rc15) on Debian. I am trying to set up virtual servers based on the principal in this thread: http://www.dovecot.org/list/dovecot/2006-October/017165.html which suggests something like this to support multiple certificates:

server foo {
  listen = 1.2.3.4
  ssl_cert_file = /etc/ssl/certs/foo.cer
}

server bar {
  listen = 1.2.3.5
  ssl_cert_file = /etc/ssl/certs/bar.cer
}

My virtual configs look like this:

server mail.domain1.org {
  listen = 1.2.3.4
  protocols = pop3 pop3s imap imaps
  ssl_cert_file = /etc/mail/hosts/domain1.org/ssl.crt
  ssl_key_file = /etc/mail/hosts/domain1.org/ssl.key
  auth default {
    mechanisms = plain
    passdb passwd-file {
      args = /etc/mail/hosts/domain1.org/userdb
    }
    userdb passwd-file {
      args = /etc/mail/hosts/domain1.org/userdb
    }
  }
}

server mail.domain2.org {
  listen = 1.2.3.5
  protocols = imap imaps
  ssl_cert_file = /etc/mail/hosts/domain2.org/ssl.crt
  ssl_key_file = /etc/mail/hosts/domain2.org/ssl.key
  auth default {
    mechanisms = plain
    passdb passwd-file {
      args = /etc/mail/hosts/domain2.org/userdb
    }
    userdb passwd-file {
      args = /etc/mail/hosts/domain2.org/userdb
    }
  }
}

but I can't get ithis to work. Dovecot starts but authorisation fails. Is this kind of setup possible - is it possible to configure different passwd-files for connections on different IPs, or am I going to have to run separate instances of Dovecot for each virtual host?

Thanks

John