just catching up on my mail after a week's vacation...
random thoughts on defining new SMTP response codes:
1. IANA should maintain the list of response codes.
2. The new SMTP document being written by DRUMS should specify the
registration procedure. (offhand, I'd suggest that the code has to be
defined in a standards-track or experimental RFC with IESG approval)
3. New SMTP codes should probably be defined only when necessary for
the the server to notify the client of a state transition....not just
for new kinds of errors. RFC 1893 codes, along with the
ENHANCEDSTATUSCODES option, should be used to communicate new kinds of
errors where no new state changes are introduced.
4. There's no problem with defining new SMTP codes if those codes will
only be generated by servers that claim to support a particular ESMTP
option, and only when a client explicitly invokes that option.
Otherwise, there needs to be a really good reason for defining a new
code...like a state change.