I woke up this morning to check one of my webmails only to discover that I can’t reply email. Whenever I try to reply any email, I get the “550 "Your IP: ::1 : Your domain is not allowed in header From” error message.
I fixed it via my WHM by editing the domain MX entry. I set the domain to use local mail exchanger instead of the automatic settings.
If that didn’t fix it for you, you can also try updating the domain nameservers via “edit DNS zone”