I guess you didn’t want my mail, then.

From a local ISP; I’m sure this seemed like a great idea at the time.

220 mx2.avalonworks.net ESMTP Postfix
helo hostname-of-internal-mailserver.mati.ca
250 mx2.avalonworks.net
mail from:<rich@mati.ca>
250 Ok
rcpt to:<test@igs.net>
554 <hostname-of-internal-mailserver.mati.ca>: Helo command rejected: Host not found

Er, sorry, what failed? I guess it forgot to tell me way back
then. I thought for a minute that it waited until RCPT to be able to
accept mail to postmaster in any case, but no, that fails there too.
I particularly like how an unsuccessful DNS lookup causes a permanent mail
failure, because DNS is always reliable.


Besides, no-one ever sends mail from a host that can’t receive mail
(say, behind NAT, maybe), and spammers would never put a resolvable
address in HELO.


On a hunch:

220 mx2.avalonworks.net ESMTP Postfix
helo mail2.igs.net
250 mx2.avalonworks.net
mail from:<rich@mati.ca>
250 Ok
rcpt to:<test@igs.net>
250 Ok

Yes, spammers would never ever just put the destination address
in the HELO. Sometimes I think antispam efforts exist to provoke
a cold war. (See also “challenge-response”).

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