AFAIK a naked IP address as domain like IPInsteadOfDomain@127.0.0.1 doesn't work (at least in some mail servers like Postfix they are bounced with a "bad addres

AFAIK a naked IP address as domain like IPInsteadOfDomain@127.0.0.1 doesn't work (at least in some mail servers like Postfix they are bounced with a "bad address syntax error). The address has to be like IPInsteadOfDomain@[127.0.0.1] and I don't see this case covered.