[Mimedefang] md_check_against_smtp_server and md_graphdefang_log

[Tilman Schmidt]

Am 26.03.2013 23:24, schrieb kd6lvw at yahoo.com:
> --- On Tue, 3/26/13, ts at phoenixsoftware.de <ts at phoenixsoftware.de> wrote:
>> ...
>> - 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.  That's what LDAP is for, but it can be done with other database types too.

Sure, in a perfect world that would be the way to go.
Unfortunately, real life tends to get into the way of such
theoretically better solutions. You did notice my mentioning
of the 'M' and 'N' words, I trust? ("Microsoft" and "Notes",
that is.)

>  With properly set up LDAP servers, one may even choose to make a subset of the information available to sending servers so they can check before even attempting to connect to yours.

I'll try to remember your advice should I ever come across a
properly set up LDAP server.

> Several MTA programs (e.g. sendmail) have had LDAP query ability built in for more than a decade.

Ever tried to make that work against a Microsoft Exchange or
Lotus Notes server? I did, and ruefully returned to SMTP
call-ahead.

> 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

Technically, yes. But again, reality gets in the way of
technically proper solutions and forces you to make do with
actually working ones instead.


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