lmtp and virtual users

[David Wells - Alfavinil S.A.]

Good afternoon.

I have dovecot setup to authenticate virtual users using either gssapi
or doind a bind to an ldap server to achieve a single sign on capable
imap server connected to a samba active directory DC. What I am also
trying to achieve is to have dovecot's lmtp daemon handle the mails
passed from postfix. However, the only way I've gotten this to work is
setting allow_all_users = yes in the userdb but this causes lmtp to
deliver mails to non existant accounts without rejection. I've been
searching but haven't found a way to set this same thing up but having
dovecots lmtp check the validity of the mails recipient against the same
samba AD DC through ldap before delivering it and rejecting unknown
email addresses. Could someone please provide some insight into how to
achieve this?

Thank you very much in advance.
Best regards,
David Wells.