DMARC support for forms?

I have email security / authentication set up on my domain (SFP, DMARC, DKIM).

When an email is sent from my website (built on Gridbox), using Forms, it is rejected by my mail system because it fails DMARC verification.

"Remote server returned '550 5.7.509 Access denied, sending domain xxxxxxx.com does not pass DMARC verification and has a DMARC policy of reject.'"

That is what I expect to happen when someone is sending email that is spoofed or does not come from me. But, when I have my email set up in Forms and send an email from it, it gets rejected.

I know when I use third-party systems to send email, such as Mailchimp, they have directions on adding a CNAME record to allow email sent from there to be authenticated.

Note, I have DMARC (and SFP, DKIM) set up and working properly elsewhere. I have the DNS records added to my domain and they test fine. My email provide (Office 365 Exchange) is set up and working properly with all three. As well as a third-party of Mailchimp. All of those sources work fine and are properly authenticated.

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