[Mimedefang] md_check_against_smtp_server and md_graphdefang_log

[kd6lvw at yahoo.com]

--- On Tue, 3/26/13, Steffen Kaiser <skmimedefang at smail.inf.fh-bonn-rhein-sieg.de> wrote:
> I wrote:
> > used to test the sender's address for validity as a
> return address.  If it were to be limited to servers
> under one's control and enforced as such, the routine would
> have to obtain the recipient's MX-RRset internally and test
> all higher priority MTAs; thus it would not need the remote
> host address parameter.  It would determine which host
> in the MX-RRset it is running on based on the macro
> variables passed in via the milter interface.
> 
> I don't agree, using the MX is necessary for external
> addresses, but for internal ones, esp. if the server does
> not relay many domains, which are managed by others, one
> usually knows the correct _internal_ maildrop host, which
> has probably no MX at all. At least one saves the DNS
> requests.

You may not agree but that is what the function is for per the author.
I agree that there are better ways (e.g. LDAP database) to do this than to fake an SMTP transaction, aborting just before the DATA phase.  When I first saw this function years ago, I thought that its purpose was to make callbacks to the sender's mailbox to test reverse deliverability, not to exclusively test the primary MX's acceptability of the message from a secondary.