I had a domain connected and working. Out of idle curiosity, I hit the test button on the M365 Mailflow page associated with one of my domains. After running for a while, it reported the test failed and changed the domain status to disconnected. The reconnect button now produces an error with a red X after signing in, the error reads "Mailflow Rules not configured. Please try again." On the O365 side I can see the rules have been created then deleted. I deleted the domain from the Mailflow settings and now cannot add it back.
Hello Justin,
Thank you for contacting the Sophos Community.
I saw this happening to a couple more users, reported and currently, this is being investigated under MD-3572
Regards,
I brought this to Support's attention, and it has been reported for "mentorship."
This can be marked as solved. It seems that waiting a day or so then trying again I was able to complete the connection.
Actually had the same thing happen to me this morning, opened a ticket but haven't heard back.