I too see the same warnings “SOA Serial Number Format is Invalid” and “SOA Expire Value out of recommended range” when checking my “email health” on mxtoolbox.com.
I exported the DNS settings and imported these to Cloudflare which excepted the records. I’m just trying to locate the record(s) where the flagged settings are but cannot find them.
How are the SOA records entered? as a txt, srv or something else?