I'm mostly a happy admin of spamassassin (3.4.0-6) + exim4 (4.84.2), setup for server-side spam-filtering on a Debian/jessie system.
Recently a user reported some false positives. On closer inspection it turns out, that the legit emails were
- sent from some dialup IP address (which gets listed in multiple blacklists)
- passed on to the mail-server of the sender's ISP (using whatever authentication they had in place), which
- then delivered the email to my mail server
- which flagged the mail as SPAM because one of the IPs in the "Received" headers was blacklisted
spamassassin matched a handful of blacklist rules (
Note that the email only got positive scores due to the IP being blacklisted.
The relevant header in the email that triggered the SPAM flagging is:
Received: from [10.126.95.175] (unknown [220.127.116.11]) by smtpfilter1.public.one.com (Halon) with ESMTPSA id ee1f1e82-251c-11e7-8f0e-b8ca3afa9d73; Wed, 19 Apr 2017 16:26:25 +0000 (UTC)
now given that:
the mail server(s) of the sender's ISP are all clean (seemingly not listed in any blacklist)
I obviously don't know how the sender proves their email legit to their ISP, but I assume that some form of authentication does take place
... I think that spamassassin should not have flagged that email as spam.
To be precise: my gut feeling tells me that spamassassin should properly add SPAM score for mails directly received from blacklisted IP addresses. However, if the mail went through a "clean" MTA (the ISP's mail servers), sa should assume that "they" (the ISP) has taken proper measures to ensure the legitimacy of the email.
Since I'm running my setup for quite some time and haven't had many false positive reports until now, I wonder:
Is the above expected behaviour?
If not, is the problem on my side (e.g. i misconfigured my spam analysis to take parts of the received-chain into account which it shouldn't. if so, where should i look for a fix?)
If not, is the problem on the ISPs side? (e.g. they should better conceal the broken IP addresses from which they accepted authorized emails. if so, should i direct complaints to them?)