RFC 2821 (RFC 2821bis) says for the NOOP:
4.1.1.9 NOOP (NOOP)
This command does not affect any parameters or previously entered
commands. It specifies no action other than that the receiver send
an OK reply.
This command has no effect on the reverse-path buffer, the forward-
path buffer, or the mail data buffer and may be issued at any time.
If a parameter string is specified, servers SHOULD ignore it.
Syntax:
"NOOP" [ SP String ] CRLF
I just came across a transaction where a Microsoft ESMTP server rejected
it with a 421 response.
The paragraph should include semantics that the NOOP command itself
SHOULD be ignored, not just the string SHOULD be ignored. Maybe:
This command does not affect any parameters or previously entered
commands. It specifies no action other than that the receiver send
an OK reply. Server SHOULD ignore the NOOP command by issueing a
250 response.
--
HLS
--
Sincerely
Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com