Re: Abort data transfer?

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
> that.
>   
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