DMARC is indeed not usable at this point, internal e-mails coming from websites that get forwarded to external get blocked when something is a little bit off by the DMARC check. There is no way to make a bypass for internal e-mails so we have to completely disable DMARC to make it all work again. Most websites and Wordpress plugins don't offer the ability to set the correct headers to make DMARC work so a bypass would be nice.

internal emails (within the same domain) don't reach their recipients any more.

-> check your hostname

We just updated to Plesk Onyx 17.5.3. After activating DMARC checking, internal emails (within the same domain) don't reach their recipients any more. There is even no error message. The emails simply get lost. After deactivating DMARC everything works fine again.

This seems to be a major bug. DMARC is not usable.

Plesk Onyx v17.5.3_build1705170317.16 os_CentOS 7:

If I enable DMARC to check incoming mail, all emails from yahoo.com are rejected.

I am very disappointed that DMARC is not in Onyx. Some examples who already has DMARC control on incoming emails: gmail.com, outlook.com, yahoo.com, aol.com. We need it in Plesk urgently!

Implementing dmarc for incoming email will help reducing spam

They just included DKIM... so we need to push for this one....

It is already in ONYX

Of course, we need DMARC as well

Yes please I am for it too

Wasn't this on the list and confirmed it was included in ONYX? Vote yes.

Please DMARC integration

I'm not sure why they separated the original DKIM/DMARC suggestion, only implemented DKIM, then sent DMARC back to be voted on again. The original suggestion was for implementation of both.