Blocking emails that claim to come from our

Drew Marshall drew at THEMARSHALLS.CO.UK
Wed Dec 7 12:25:03 GMT 2005

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On Wed, December 7, 2005 11:51, Dhawal Doshy wrote:
> minuscule correction
> 'reject_invalid_hostname' under 'smtpd_helo_restrictions' will simply
> reject the 'helo' if it contains any special / bad characters..
> The parameter you are talking about is reject_unknown_hostname, which
> will reject the mail if no valid A/MX record exists for the helo
> hostname and causes quite a few false positives.
> see:

Yes, you are right. Sorry that's my fault for not reading (Or is that
thinking!) properly.

It can get slightly more complex than that even as you can reject on
client address using smtpd_client_restrictions (Which is also where you do
the RBL checks, for the record) with reject_unknown_client or more
leniently reject_unknown_reverse_client_hostname (If you are running 2.3)
as that will check on the client not what it helo's as.

One of the beauties of Postfix is the ability to run these restrictions at
various different stages of SMTP conversation, client, helo, sender and


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