[Mailman-Users] DMARC and Gmail
addw at phcomp.co.uk
Wed Apr 16 18:55:12 CEST 2014
On Thu, Apr 17, 2014 at 01:27:23AM +0900, Stephen J. Turnbull wrote:
> There are several possibilities. One is that DMARC doesn't define the
> semantics of "reject". (Why doesn't that surprise me?) Here's what
> they say:
> 15.4. Rejecting Messages
> This proposal calls for rejection of a message during the SMTP
> session under certain circumstances. This is typically done in one
> of two ways:
> o Full rejection, wherein the SMTP server issues a 5xy reply code
> as an indication to the SMTP client that the transaction failed;
> the SMTP client is then responsible for generating notification
> that delivery failed (see Section 4.2.5 of [SMTP]).
> o A "silent discard", wherein the SMTP server returns a 2xy reply
> code implying to the client that delivery (or, at least, relay)
> was successfully completed, but then simply discarding the
> message with no further action.
> Each of these has a cost. For instance, a silent discard may
> prevent "backscatter" (the annoying generation of delivery failure
> reports, which go back to the RFC5321.MailFrom address, about
> messages that were fraudulently generated), but effectively means
> the SMTP server has to be programmed to give a false result, which
> can confound external debugging efforts.
They should have allowed/defined a new 2xy code that could be returned, eg 253
which means ''Mail accepted but will be discarded''. So a simple sending MTA could
just look at the initial '2' and think 'job done', a more complex one could note
that the receipt wasn't quite right.
However: it still means that some people on mail lists occasionally don't get
stuff - this will cause confusion at best or could be dangerous (if the mail
list has a critical function).
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