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Re: Abort data transfer?

2009-10-20 23:04:33

Paul Smith wrote:
David MacQuigg wrote:
Forget about DKIM.  What if there is some other reason to abort, like
the payload is too large?  We cannot just continue receiving data
forever.  Is there a "permissible" way within SMTP to abort during
data, or should I just ignore these ambiguous requirements, and
either: 1) Send a TCP reset, or 2) Let the transmitter hang.
I would just continue accepting the message, and throw away the data,
then give a 'message too big' error at the end.

This doesn't deal with the case where the data never stops.

I suppose you could try to be clever and do a grey-listing-style thing
of recording the IP address, sender & recipient, and dropping the
connection, then when the retry is done, reject the message before the
data is sent - but I wouldn't be too confident about the reliability of

Good suggestion. The IP address is all we really need to identify the transmitter, however. We need to allow at least 3 retries, in case the sender is legit, and trying to fix a problem. After that, I don't think anyone should complain about having their transmitter blacklisted for a day or two. If it takes more than 3 tries (or some other measure, like total minutes the receiver has been listening to crap) if it takes more to fix the problem, they shouldn't be practicing on our client's receiver.

We could set up a special test server just for such practice. Any message to that server gets a nice reply with complete diagnostics on any problems we find with their authentication setup, maybe even a history of problems from that transmitter, in case they don't know why they were blacklisted.

Yes, we could separate different message streams based on sender & recipient addresses, and it wouldn't be that much extra work, but then our rejects and domain ratings are more likely to be ignored. The Transmitter Agent (operator of the outgoing border MTA) is responsible for problems generated by his clients. Most legitimate operators are honest and competent, and the mail from their transmitters is never a problem. The few who have problems may be incompetent, or they may feel they have business reasons to allow the abuse. It doesn't matter what the reason. If lumping all their customers together is unfair to some, they should put pressure on their agent to fix the problem, or find another agent. A Transmiter Agent can insist that his clients follow acceptable practices, and can provide per-account rate limits and other measures to help their clients avoid abuse by individual accounts.

-- Dave

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