On 4/22/2014 5:30 PM, Martin Rex wrote: >> Why is there such a recommendation? What is a mail receiver? I am >> > asking the question as there is "receiving SMTP server" in that sentence. > That would be silly. RFC5322.From might contain no DNS domain to begin with. That was legal for RFC 733. Apparently I dropped it for RFC 822. The idea of an online surrogate (Sender:) for an offline author (From:) was a friendly construct, but it didn't prove useful. So a From: field address with no domain name has never been valid for "Internet" email. d/ -- Dave Crocker Brandenburg InternetWorking bbiw.net