Is it possible you can find some time to adjust the expression check code to allow the underscore _ in creating a TXT DNS resource record, so that a "_dmarc" resource record can be added to a domain name and go along with proper spf and dkim checking?
Your dkim plugin creates one similar called mail._domainkey, so why not alter the code regex character check to not allow funny chars unless matches '_dmarc' or regular characters.
I AND my clients need it for reasons including abilities to track phishing and spam, as well as ability to allow a sender to indicate that their emails are protected by SPF And/Or DKIM implemented on the servers, more as well as making it More Probable, no email is delivered to SPAM boxes instead of Inbox es when it is Legitimate Email.
Checking the below link, errors with message;
DMARC record published in the wrong place!
If you're the owner of this domain, your DMARC record needs to
discoverable at _dmarc.mydomains.com, and not at mydomains.com. The
"_dmarc." part is required!