Re: custom auth

rootdn "cn=admin,ou=users,dc=mail"

access to attrs=userPassword by anonymous auth by * none

How do I tell OpenLDAP to authenticate against cn=<login>,ou=users,dc=mail and its userPassword attribute?

You don't. You've got the wording a bit wrong. :-) Your configuration will allow an LDAP client to authenticate against this OpenLDAP instance with a user defined in your directory. Supposing you have an entry

dn: cn=mta,ou=users,dc=mail cn: mta userPassword: <something> objectclass: person sn: mta

What you probably want to do is to tell your LDAP client (your MTA?) to bind to OpenLDAP as "cn=mta,ou=users,dc=mail" with that entry's password.

-JP