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Re: Mail Data termination

2011-08-21 08:18:41

On 21/08/2011 13:21, Alessandro Vesely wrote:
Its a selfish idea from the standpoint that it considers its own benefits by
ignoring the impact at the receiver. But I do think its a useful method if
its prearrange with the receiver in the same way we white list specific
senders (i.e, Allow Relay IP tables, smart hosting, etc).
It is not selfish, since per-connection costs are experienced by receivers too.

If the receiver does load limiting by restricting the number of open connections, then it is selfish for the sender to presume that it can keep hold of one of these connections for longer than necessary.

I agree that a few seconds is probably not significant, but if 5 seconds grows to 15 seconds, then 60 seconds etc, then it could become a big issue for some servers. OK, so the senders are also having larger numbers of open connections, but this is under their control, not the receiver's.

The sender also has the privilege of being able to decide when and what to send, whereas the receiver has to respond in a timely manner to the sender's requests - thus the sender is under much less pressure than the receiver. The sender can keep 1000 connections open and know that it will only send to one at once, but if the receiver has 1000 connections open it has to be able to respond to all of them quickly, even if all 1000 decide to send a message at the same time. The receiver has to respond quickly, to stop the sender (which generally use very short timeouts, regardless of what 5321 says) from timing out prematurely and retrying unnecessarily.

So, the per-connection cost is NOT the same for the sender as for the receiver, it is much cheaper for the sender.

For the receiver to unilaterally 'close the longest idle' connection, as has been suggested before, risks penalising slow senders while not affecting those which are deliberately being greedy, and would also be 'frowned upon' by RFC 5321 which says the server should have a timeout of at least 5 minutes. (It's allowed for it to be shorter, but why would the 5 minute figure be documented, unless it should be stuck to?)

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