I've tried and drawn the consequences of defining VHLO (verified
hello) or IAGG (I'm a good guy) as an SMTP extension, as John
suggested a while ago. The I-D is at
Incidentally, writing the I-D I've found a pair of possible nits for
5321bis, which may be worth amending:
* The extension definition in section 2.2.2 (lines 534-561 in the
numbered draft) don't mention that each extension should explicitly
specify if it is valid on the Submission port.
* There is no IANA registry of all defined MAIL (or RCPT) parameters:
it may become a problem for future extensions authors willing to check
that a new parameter doesn't conflict with existing ones...