Setting Sendmail to Refuse Possibly Forged Headers

antenneX antennex at
Thu Apr 15 20:13:55 PDT 2004

----- Original Message ----- 
From: "Dan Nelson" <dnelson at>
To: "Martin McCormick" <martin at>
Cc: <freebsd-questions at>
Sent: Thursday, April 15, 2004 12:26 PM
Subject: Re: Setting Sendmail to Refuse Possibly Forged Headers

> In the last episode (Apr 15), Martin McCormick said:
> > The sendmail that comes with FreeBSD is set to disallow all
> > third-party relaying which is wonderful and how I want to keep
> > things.
> >
> > In addition to that, I would like to try to set it to refuse
> > incoming mail with forged address headers.  Judging from the logs, it
> > seems to be pretty good at catching such messages and most of the
> > ones I look at that trigger this warning are spam.
> Take a look at the milter-sender port, which checks the sender's email
> address and verifies that an smtp server is listening.  It's not
> something that can be done within sendmail, which is why it's a milter.
> Another thing to check is the HELO string.  The following will block
> all incoming mails claiming to be the mailserver itself.  Replace
> XXXXXX your with server's IP and domainnames, spearated by spaces (so
> "C{RejectHelo}", for example).  I deny ~500 spams
> a day with this rule alone.
> #+\/+ Block connections from servers that try and send our IP or hostname
in the HELO
> C{RejectHelo} XXXXXXXXXX
> SLocal_check_mail
> R$* $: $1 $| $&s Put helo name in workspace
> R$* $| $={RejectHelo} $#error $@ 5.7.1 $: "550 Spammer access denied"
> R$* $| $* $: $1 Extract helo from workspace if it doesn't match
> #-/\-
> -- 
> Dan Nelson
> dnelson at

Dan: Your suggestions here were appealing, but I'm batting zero.

1- Will milter-sender work alongside spamass-milter...??
    I *think* it was working on a test box, but failed on production box.

2- Each of your 3 lines above for "local_check_mail" yelled about expecting
a Tab when sendmail was restarted... not sure how to fix that.....

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