How not to be a spammer [4]: say HELO

How can legitimate direct marketers get their messages through more reliably? How can they avoid being branded as a "spammer" by over-enthusiastic spam vigilanties?

We wrote about this problem before. See [1] and [2]. This is the second of an irregular series of blog posts where we'll examine some additional ideas. the first post of the series is here[3].

SMTP or ESMTP transactions always start with a HELO or EHLO command sent by the sending mail server. This command identifies the sending host to the receiving host. The recommended identification is the senders FQDN (the Fully Qualified Domain Name, e.g. mail.example.com).

By convention, this identification infomation is only logged, and not checked. This convention has caused many senders to get lazy.

Increasingly, spam filters are checking the information, and cross-checking it against the IP address of the sender. Mis-matches will cause the message to be rejected (or at least make it more likely).

We recommend that senders ensure that their sending IP address not only has a valid PTR record, but that PTR exactly matches the name given in the HELO command.

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