[Mimedefang] md_check_against_smtp_server and md_graphdefang_log

[David F. Skoll]

On Tue, 26 Mar 2013 15:24:17 -0700 (PDT)
kd6lvw at yahoo.com wrote:

> --- On Tue, 3/26/13, ts at phoenixsoftware.de <ts at phoenixsoftware.de>

> > - The easiest way for that is SMTP call-ahead aka
> > md_check_against_smtp_server.

> A much better way is to access the user database directly.

Yes, but that may not be possible for policy reasons.  Our spam-filtering
service filters mail for a number of clients who (obviously) are willing
to open up TCP/25 for us, but are far more reluctant to expose their
LDAP directory to us.

[...]

> Technically within SMTP, the proper way for a secondary to check with
> a primary for valid users would not be by faking a mail transaction
> but by using the VRFY or EXPN commands (which may be restricted to
> only the secondaries to prevent outside abuse).

Almost all SMTP servers are configured not to support VRFY or EXPN.

Regards,

David.