On Tue, 13 May 1997 17:59:40 -0700 "Paul E. Hoffman"
And now for something completely different. I needed a new SMTP response
code for an SMTP extension I'm writing. However, I could not find any
central registry of them. This seems to be a bit of a problem, because I
don't want to choose the same one that some other extension writer has
Unfotunately, we have a number of implementations that
believe that the only valid codes are those that are in 821
-- every time a new one has been added, there has been
trouble. Conversely, one or two implementations have
promiscuously implemented all sorts of codes without
documenting them. This was a reason why the "be prepared
to use first digit only" rule went into RFC 1123 (perhaps
the main reason).
Consequently, much as a code registry would be a good idea
--and IANA is probably the right place-- you might as well,
in practice, just make something up and assume that only
the first digit will be relevant.
There is a case to be made for trying the following
* Make up one more set of codes, e.g.,
299, 399, 499, 599
And give them the definition "extended code of
status/severity (2, 3, 4, 5), see extended reply
code" and a phrase syntax of "n.n.n text".
* Make absolutely sure that the definitions and extension
mechanisms of RFC 1893 are adequate.