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Re: [ietf-smtp] Per-Recipient Data Responses

2014-03-05 15:38:19

On Wed, Mar 05, 2014 at 08:22:19PM +0000, Paul Smith wrote:
On 05/03/2014 18:20, Murray S. Kucherawy wrote:
How come this never got adoption?  It comes up from time to time
in "We really should do this" sorts of discussions, but it doesn't
seem like anyone ever took the plunge and it just expired.  Is it
just that nobody does it because nobody else does it?

Hmm, this one's a tricky one. With our mail server we've been quite
careful to do things which would either accept the "whole message",
or reject it all.  I can see places where we could change
functionality to use PRDR, but the problem is that the user would
expect it to always work, not be dependent on the sending MTA. So,
we would have to 'fake' PRDR, by falling back to accepting the
message and generating bounce messages, which isn't nice, and will
lead to backscatter.

Correct me if I'm wrong, I may have missed something in the draft:

PRDR implies that deliveries be attempted during the SMTP transaction so
this cannot really be implemented by MTA that use a two-step approach to
first commit to queue and acknowledge responsibility, then later deliver
the message to the mailbox ?

No, that's incorrect. From the draft:

           Furthermore, positive responses are not a
           guarantee that any subsequent transfer or delivery operations
           will also succeed, but instead only indicate that the message
           appears to be acceptable for the recipient according to the
           rules and policies that are known to the current server.

You should do as much vaidation as possible before accepting an address or
message, but that's true in general; it has nothing to do with this

More generally, any notion that this extension eliminates backscatter is 
incorrect for a whole bunch of reasons, this included. At most it limits it a


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