@alento Sorry that I was not clear. I do want to continue using an external dns unless it overcomplicates things. (I have quite a few subdomain records in place and would like to wait to migrate them until I have had a chance to use MiaB)
On the status check i see. the follwoing error:
This domain should resolve to your box's IP address (A yyy.yyy.yy.yy) if you would like the box to serve webmail or a website on this domain.
The domain currently resolves to xx.xx.xx.xx in public DNS.
It may take several hours for public DNS to update after a change.
This problem may result from other issues listed here.
From this I gather that an A record for the second level domain (with no subdoomain) needs to be directed at MiaB. What custom dns entry would meet the needs of the status check without requiring migrating to MiaB for my DNS? (But also allowing me to recieve and send mail at firstname.lastname@example.org)