John C Klensin <john+smtp(_at_)jck(_dot_)com> wrote:
The example, as written, is simply invalid. SMTP does not allow
single-labels domains. They are explicitly prohibited in 5321 and its
predecessors.
That is incorrect. The syntax in RFC 5321 is
Domain = sub-domain *("." sub-domain)
Whereas in RFC 2821 it is
Domain = (sub-domain 1*("." sub-domain)) / address-literal
And in RFC 821 it is
<domain> ::= <element> | <element> "." <domain>
It was generally agreed that the 1* in RFC 2821 was an editorial mistake
which was fixed in RFC 5321.
Tony.
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