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Re: Mail Data termination

2011-08-19 08:49:29

Sorry Ned, I was referring to the "cheaper" part claim. Your recognition for a shorter idle residence time, cache time, was previously noted.

I have yet to compare notes with customers. Among the top senders is FaceBook's mailer with a 5 mins delay before sending QUIT. It looks like Hoffman's mailer setup has a 4 mins delay and there are others from unknown senders. So its apparent now where these odd unexplained delays are now coming from - Connection Sharing clients.

Well, I can't stand for this. A local policy option to lower the server idle client timeout to 1 minute (default) after the 1st transaction has been finished will be provided. I'm calling it Final-Idle-Time. Probably also look at some tuning logic to monitor Sender vs Final-Hold-Time to see if that can be used to kick out idle clients when new connections come in. This is part of the problem that a CS logic does - increases cost on receivers to avoid the potential problems caused by them, and that includes contributing to any DoS attacks.

ned+ietf-smtp(_at_)mrochek(_dot_)com wrote:

ned+ietf-smtp(_at_)mrochek(_dot_)com wrote:

>> I don't think the practice of connection caching is particularly selfish when >> compared to the cost of having the connection torn down and then re-established >> with some frequency, when it's generally much cheaper for both the sender and
>> the receiver to just leave it open.
> Exactly. Although it is necessarily up to the client to decide, the server also
> benefits as long as the connection isn't cached for very long.

I can see this when two systems have prearranged dedicated channesl
for high load exchanges, but in general, I disagree that it is
"cheaper" and definitely not for the receiver. I don't see how that
can be justified. Average SMTP session times last year of 10-15
seconds are now up to 4-7 minutes this year  Thats better?

Please reread my message. Nowhere did I say that clients should cache
connections up to the 5 minute timeout - in fact I said the exact opposite:

 Caching a connection for anything even close to five minutes is almost
 certainly counterproductive - SMTP connection establishment isn't *that*
difficult. But holding on to a connection for just a few seconds can be quite
 beneficial for systems handling high volumes of mail.

I have no idea why your servers are seeing longer averages, but I can assure
you it isn't our client that's doing it. When there are no more messages we
only keep connections open for a few seconds and this is not configurable.



Hector Santos

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