On Thursday 18 March 2004 05:43, Neil Brown wrote:
It is really up to the MTA whether it does anything else with the mail
message in any of these cases, and in particular it might choose to
successfully deliver the message after returning 5xx (just as it might
choose to dump a message after a 2xx if it turned out to be pure virus).
That's true. My own MTA returns a 5xx response after the DATA and stores a
copy in a temporary junk mail folder.
One example where I feel it would be particularly useful is on
receiving a message where we aren't confident enough of its badness to
reject it, but we also aren't confident enough of the envelope-from to
be comfortable sending a DSN if it turns out there is a failure later
on in delivery.
In that case one might respond to the '.' terminating DATA with
555-Message accepted for conditional delivery.
555-Due to lack of a reliable return address, subsequent failure
555-will not be reported.
555 See http://what.ever/555.html for more details
I have tried this but in general the sending MTA mangles the reponse so badly
that non-technical users just get confused.
The approach I use is to use spf-guess criteria to decide wether to send a
bounce - if guess fails then I try to return a meaningful 5xx response like
the above instead of annoying a third-party. If spf is unknown but spf-guess
succeeds I can send a challenge-response because the return-path is most
likely OK.
It would be great to have some way to say that a response is supposed to be
user-friendly, for example an RFC2822 format message! But sadly such a
feature does not exist. Maybe time for another ESMTP extension?
- Dan