That sounds like a job for Spamassassin AskDNS plugin ->
https://spamassassin.apache.org/full/4.0.x/doc/Mail_SpamAssassin_Plugin_AskDNS.html
You could query _SENDERDOMAIN_ for MX and act if the MX is in your
defnied list of "bad" MX hosts. Though I'm not sure if _SENDERDOMAIN_
is Env oder Header based. My stomach sez it's Env based ;-) so one
could use _AUTHORDOMAIN_ for header based check.

Cheers

tobi

On Fri, 2025-11-07 at 08:04 +0100, Benoît Panizzon wrote:
> Hi Assassins
> 
> I noticed a increase of scam mails expecting the victim to reply and
> disclose personal data, which originate from daily changing domain
> names and sending ip addresses (probably a botnet).
> 
> To name those received this week:
> 
> gutter-install-info.site
> sd-st.com
> auto-repairhelp.xyz
> 
> common to those domains is the MX used:
> 
> mx1.privateemail.com
> mx2.privateemail.com
> 
> operated by our good spam friend namecheap.
> 
> Is there a way or plugin which would allow to score based on the MX
> of
> the sending domain?
> 
> I contacted namecheap about their system being abused - but as usual
> I
> got stuck at the 'please log in to your account to open a case - oh,
> you
> are not a customer - sorry then we can't help'.
> 
> -- 
> Mit freundlichen Grüssen
> 
> -Benoît Panizzon- @ HomeOffice und normal erreichbar

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