LMTP tcp listener with auth?

[Andreas Thienemann]

I am wondering if it's possible to have a tcp listener for LMTP do 
authentication and not accept any unauthenticated mail.

My configuration looks like the following:
service lmtp {
  inet_listener lmtp {
    address = 192.168.0.1 127.0.0.1
    port = 24
  }
}

This gives me a network reachable lmtp socket, but of course no 
autentication. When reading the docs, it seems though that only userdb 
lookup and no actual authentication is supported?

Is that understanding correct?

cheers,
 Andreas