Re: Mail Data termination

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?)