On 05/03/2014 21:25, Gilles Chehade wrote:
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 correct (AIUI) - all is fine if the sender support PRDR.
The problem is that if users expect PRDR functionality to be there, you
can't have it work sometimes and not others. So, when the sender doesn't
support PRDR, the receiver needs to fake it by first accepting the
message for all recipients and then sending delivery failure reports back.
Otherwise, one user could say "reject a message if it it contains the
word 'viagra'" and another could want to accept i. Then, sometimes the
first user would have the message rejected (if it is just to them, or
the sender supports PRDR), and sometimes they would receive the message
(if it is to both users, and the sender doesn't support PRDR). Users
wouldn't be happy about this inconsistency, and the support load would
be unacceptable from our PoV.
So, if the sender didn't support PRDR, we'd have to accept the message,
deliver it to the second user, and send a bounce message back (with risk
of backscatter) for the first user.
In any case, spammers would probably not support PRDR, and that'd
probably be the most common case people would use it, and that would be
the most likely case to cause backscatter from accepting then sending
Paul Smith Computer Services
Tel: 01484 855800
Vat No: GB 685 6987 53
ietf-smtp mailing list