On Oct 11, 2011, at 1:45 PM, Steve Atkins wrote:
In that case, some minor extension to allow the SMTP server to
communicate something a bit more nuanced than "Go away, come back
later." might have some value.
I could see value in that. I could imagine an SMTP extension which,
if included, indicated that the server might send a response of the
form
4xx please retry between <date-time>-<date-time>
...in response to say the MAIL (or maybe DATA) command, where
<date-time> could be an ISO8601 date-time (the horror!) based on GMT
(Z) and with no punctuation. If the client included a SIZE the
server could even do bandwidth reservation. Of course there would
be no guarantee that the second attempt wouldn't result in some sort
of 4xx response for other reasons.
Greylisting servers could certainly make use of it, though I don't
know if it would be a good idea to recommend that greylisting
servers use it.
Keith