SMTPUTF8 issue 1: UTF8 use in address fields

[arnt]

Hi,

EAI allows From:/To: etc to contain UTF8, but forbids nothing. This means that From: Grå <grå@xn--gr-zia.org> is legal.

Please detect whether any address fields use xn--. The alternative is none, which includes messages that don't need/use EAI at all.