Amavis / Spamassassin – Resolving FORGED_SPF_HELO and SPF_HELO_PASS

amavisspamassassinspf

I have a web server that sends out webform type emails via Postfix 3.3.0. No inbound. No extras.

Receiving mail server is running same Postfix (but with amavis-new/spamassassin + dovecot/etc). These are both on the same domain, but different subdomains ('www.' & 'mail.').

When a test email is sent (using postfix sendmail command) from web server to mail server, everything is perfect except for the scoring on the HELO/EHLO. I keep getting a FORGED_SPF_HELO. I've never encountered this one before and there is little documentation to be found. Seems self-explanatory, though, that it is not passing SPF lookup on HELO.

The original DNS was simply 'www.' as CNAME to apex A record.
The apex SPF includes the 'a' record: "v=spf1 a mx ~all"

The HELO from log is:
helo=www.example.net, Tests:[ALL_TRUSTED=-1,FORGED_SPF_HELO=1,MISSING_HEADERS=1.207,MISSING_SUBJECT=1.767]

I adjusted the 'www.' record so it was an A record and added an SPF TXT record for it separately.

Now I get: helo=www.example.net, Tests: [ALL_TRUSTED=-1,FORGED_SPF_HELO=1,MISSING_HEADERS=1.207,MISSING_SUBJECT=1.767,SPF_HELO_PASS=-0.001]

Forged and Passed?

Main question:
Can anyone explain why in first instance the a in the SPF isn't allowing the CNAME 'www.' to pass? Secondarily, can anyone explain how you can have a "forged" and "pass" at same time?

Best Answer

The rule FORGED_SPF_HELO came from Spamassassin updates. By grepping your configuration folder (/var/lib/spamassassin at least on Debianoids) you'll see the definition:

meta    FORGED_SPF_HELO     __HELO_NOT_RDNS && SPF_HELO_PASS && !SPF_PASS
header  __HELO_NOT_RDNS     X-Spam-Relays-External =~ /^[^\]]+ rdns=(\S+) helo=(?!\1)\S/
header   SPF_PASS           eval:check_for_spf_pass()
header   SPF_HELO_PASS      eval:check_for_spf_helo_pass()

You fail rule __HELO_NOT_RDNS (the reverse DNS lookup for the host www.example.net is not www.example.net) and you don't have SPF_PASS (the host is not authorized to send e-mail on behalf of your domain).

Since you certainly don't want to add www.example.net to the list of your official mail server, configure it to send e-mails with senders of the form user@www.example.net.

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