Greg Connor wrote:
domain-spec = macro-string domain-end
domain-end = ( "." toplabel ) / macro-expand
[...]
Is that true, that we cannot use domain names without a dot
in them?
Yes, same as in RfC 2821, you cannot use FQDNs without dot in
SMTP (maybe 2821bis will fix this allowing a trailing dot).
I wonder if mx:ws. would pass the ABNF or various parsers?
No, the required dot comes before the <toplabel>, see above.
Of course TLD ws can have a sender policy just saying mx, but
nobody else could use mx:ws / include:ws / a:ws / redirect=ws
etc. The sender policy would be pretty useless, because any
HELO ws / EHLO ws / MAIL FROM:<xyz(_at_)ws> is a 2821 syntax error.
Bye, Frank