Raymond Keller:
> I configured reject_invalid_helo_hostname and was surprised to find
> that underscores were permitted. Judging by the source (I'm not
> conversant in C), it looks like the author had this comment
> regarding allowing underscores: "grr.." I feel similarly. Is that
> you, Mr. Venema? My sympathy. I take it that allowing underscores
> is for the sake of handling Windows MUAs?
Hostname syntax is defined in Internet RFCs. Postfix's hostname
validator routine cites RFC 952, RFC 1123, RFC 1035, RFC 2373.
However, not everyone reads internet RFCs before implementing email
software. In order to be useful, Postfix allows for common
deviations. The primary mission of Postfix remains to deliver mail.
Wietse
