My work email is public since it’s thoughtfully published by the Nevada/Louisiana bar associations, and judging by the amount of spam I get, frequently scraped. So my email domain has a “strict” dmarc policy that rejects spf and dkim failures. My spf only authorizes mail from the host pointed to by my mx record, and all emails from my host are signed by my dkim key.
Consequently, my domain’s postmaster account gets daily dmarc reports from google and others. But the reports have always been spf and dkim pass -> take no action (legit mail) or spf and dkim fail -> reject (probably a spammer masquerading as me).
About a week ago, I got a report from google that was spf fail, dkim pass. In 5 years of hosting my own email, I have not run into this situation.
<?xml version="1.0" encoding="UTF-8" ?> <feedback> <report_metadata> <org_name>google.com</org_name> <email>[email protected]</email> <extra_contact_info>https://support.google.com/a/answer/2466580</extra_contact_info> <report_id>1881472039149147891</report_id> <date_range> <begin>1553817600</begin> <end>1553903999</end> </date_range> </report_metadata> <policy_published> <domain>cliffordburnslaw.com</domain> <adkim>r</adkim> <aspf>r</aspf> <p>reject</p> <sp>reject</sp> <pct>100</pct> </policy_published> <record> <row> <source_ip>188.8.131.52</source_ip> <count>1</count> <policy_evaluated> <disposition>none</disposition> <dkim>pass</dkim> <spf>fail</spf> </policy_evaluated> </row> <identifiers> <header_from>cliffordburnslaw.com</header_from> </identifiers> <auth_results> <dkim> <domain>cliffordburnslaw.com</domain> <result>pass</result> <selector>201808</selector> </dkim> <spf> <domain>cliffordburnslaw.com</domain> <result>fail</result> </spf> </auth_results> </record> </feedback>
The address of the host sending the mail to google was 184.108.40.206 which is not the A record for the host pointed to by domain’s mx record.
The ptr record for 220.127.116.11 suggest it’s a cox address:
[email protected]:~$ host 18.104.22.168 22.214.171.124.in-addr.arpa domain name pointer dukecmfep02.coxmail.com.
Searching through my logs, the day before the report came in, I sent an email to a client with a cox address:
Mar 29 12:01:07 mail-server-2 postfix/submission/smtpd: connect from unknown[fd00:8000::1] Mar 29 12:01:07 mail-server-2 postfix/submission/smtpd: Anonymous TLS connection established from unknown[fd00:8000::1]: TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits) Mar 29 12:01:08 mail-server-2 postfix/submission/smtpd: 567BD140ED1: client=unknown[fd00:8000::1], sasl_method=LOGIN, [email protected] Mar 29 12:01:08 mail-server-2 postfix/cleanup: 567BD140ED1: message-id=<[email protected]> Mar 29 12:01:09 mail-server-2 postfix/qmgr: 567BD140ED1: from=<[email protected]>, size=2158, nrcpt=1 (queue active) Mar 29 12:01:11 mail-server-2 dovecot: imap-login: Login: user=<[email protected]>, method=PLAIN, rip=fd00:8000::1, lip=fd00:8801:2909:6000::c441, mpid=24017, TLS, session=<DwhUS0CFTtn9AIAAAAAAAAAAAAAAAAAB> Mar 29 12:01:11 mail-server-2 postfix/submission/smtpd: disconnect from unknown[fd00:8000::1] ehlo=2 starttls=1 auth=1 mail=1 rcpt=1 data=1 quit=1 commands=8 Mar 29 12:01:12 mail-server-2 postfix/smtp: 567BD140ED1: to=<***email@example.com>, relay=mx.coxmail.com[126.96.36.199]:25, delay=4.4, delays=0.9/0.01/2.8/0.67, dsn=2.0.0, status=sent (250 2.0.0 9wkXhMI9sYLKf9wkZhasxm mail accepted for delivery) Mar 29 12:01:12 mail-server-2 postfix/qmgr: 567BD140ED1: removed
But 188.8.131.52 is not address associated with mx.coxmail.com:
[email protected]:~$ host mx.coxmail.com mx.coxmail.com has address 184.108.40.206 mx.coxmail.com has address 220.127.116.11 mx.coxmail.com has address 18.104.22.168 mx.coxmail.com has address 22.214.171.124
If this were a dmarc report from cox, I would archive the email and promptly forget about it. But what has me puzzled is trying to figure out why google sent the report.
I understand that the dmarc reject policy does not kick in unless both spf and dkim fail. And it occurs to me if cox’s server just forwarded the exact email then the dkim would pass, but obviously the spf check would fail. But I cannot think of a scenario where that would legitimately happen.
So if you made it all the way to the end of this, I guess my question for a more experienced email veteran, is this in fact unusual? Or is there an innocuous explanation that I simply lack the imagination to find?