Keith Moore wrote:
RFC 2822 permits (as did 822) a quoted string which
consists solely of a pair of DQUOTE characters. It's
not clear what the semantics of that are or ought to be.
it doesn't have to have semantics, since quoted-strings
can be used in places where they are opaque. if someone wants their
email address to be ""@example.com this is perfectly legal.
OK, I'll buy that (at least 2821 and 2822 are consistent
in permitting it).
Likewise, a domain literal can consist solely of the
square brackets.
so? there are lots of addresses which are valid syntax but
not valid because the domain is not defined or the IP
address (in the domain literal) does not exist or is not
assigned to a host.
I'm not sure that there aren't MTAs or MUAs that would
break or pass bizarre requests to DNS when trying to
deal with [] as a domain literal.
Also, in this case 2822 seems to be alone in permitting
that syntax, which is not permitted by 2821 or 1123.