[opendmarc-users] opendmarc and Mailer Daemon

[postfix at ptld.com]

> On Mon, 2021-09-06 at 14:18 +0200, kzkz at poczta.onet.pl wrote:
> 
> I have installed and configured opendmarc on the receiving SMTP
> server.
> 
> I have noticed behavior such as the following: when the message is
> from Mailer Daemon - when 'MAIL From: <>' is used during the SMTP
> dialog, and the From: header line is a valid sender's domain,
> opendmarc marks such messages as 'dmarc=fail'. Consequently, when the
> sender's domain DNS _dmarc record contains p=quarantine/reject, the
> mail will not reach the recipient mailbox.
> 
> Does running opendmarc on the receiving server prevent receiving
> messages from Mailer-Daemon?
> What should I do to get my users to receive such messages?


You can create an SPF record for the smtp mail server so it passes 
without having a mail-from address. Lets say you have a SPF record for 
your domain example.com, it would look like this:

     example.com.   IN TXT   "v=spf1 a mx -all"

Lets pretend the PTR and Helo hostname for your mail server is 
smtp.example.com, you would add another SPF for that which looks like:

     smtp.example.com.   IN TXT   "v=spf1 include:example.com -all"

This way when the senders mail-from is <> openDMARC would pull SPF for 
the hostname `dig txt smtp.example.com.` which will tell it to grab the 
SPF it would have if there was an email address from user at example.com. 
SPF passes and dmarc should pass.