spf-discuss
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Re: SPF and SMTP 551/251 result codes.

2004-03-26 12:47:55
On Fri, 2004-03-26 at 14:34 -0500, Theo Schlossnagle wrote:
Both seem completely legitimate to use.  After all, it's your mail 
service and your rules.  The flip side of this is that the owner of that 
.forward file might be pretty upset to learn that you are an 
"uninterested third party".  Perhaps not -- it is something you'd need 
to consider.

The owner of that forward file is more likely to be upset by the fact
that sender of the mail has effectively forbidden me from forwarding 
the mail intact, as mail hosts have done for decades.

SRS is a fairly ugly hack to work around that breakage, and it's not
something which is going to be acceptable to the owners of many
forwarding hosts who don't see a future in SPF.

It would aid the adoption of an SPF-compatible world if we could give
forwarding hosts an easier option. That's what this is.

Instead of _forcing_ the forwarding hosts to either adopt SRS or break
SPF, we can punt the problem back to the sender who publishes SPF and
has actually opted in to the Brave New World. This seems reasonable
enough -- after all, it is a problem of their _own_ making. So not
expect that a sender publishing SPF records will at least react
appropriately to '551' and send the mail to its final destination for
themself, since they are claiming that I may _not_ do so?

_Personally_, I'm happy enough to reject it with a 551 result code
whether I expect them to cope or _not_.

But if you read what I posted, you'll see that I was suggesting that we
make appropriate response to a '551' result code mandatory for
SPF-publishing senders, so that I _can_ give 551 result codes with a
reasonable expectation that the mail won't be lost.

It's quite simple -- if you say a third party can't forward the mail,
you have to be prepared to do it for them.

-- 
dwmw2