Re: Mail Data termination

Murray S. Kucherawy wrote:

> > > One of the more ubiquitous MTAs out there has a feature called
> > > "connection caching" where it will keep some fixed number of outbound
> > > SMTP connections around, cycled using an LRU method, in case a new
> > > message arrives that is routed to a recent destination to avoid the cost
> > > of making a new connection and doing the initial SMTP negotiation.
> > I believe Postfix and Exchange can do this.
> And I was referring to Sendmail.
>
> The more SMTP clients there are that do this, the more likely it is that 
> a server demanding QUIT before scheduling a delivery attempt will lose 
mail.

Fortunately, that is *never* the case hence there is no problem until 
you try to correct a problem.  It helps with robustness by reducing 
problematic transactions, especially the exploited ones.
But you did highlight something I need to look at, not because of 5321 
required QUIT which by the way is only going to be addressed with YASO 
(Yet Another Server Option),  but rather analyze what the major 
dangerous presumptions and selfish engineering considerations a client 
operating under a Connection Sharing (CS) mode imposes on receivers. 
It might explains some situations seen.
First, a server may have Receiver Loading Limits and a client with a 
tenacity to take up more CPU time than it needs can get it flagged. To 
use CS for the purpose to reduce its redundancy without considering 
the load it places on receivers is a very selfish engineering 
consideration. Chewing up a channel unnecessarily for 5 minutes 
disallowing other clients connection access increases system available 
and scalability problems.
Second, it uses a dangerous presumption that a server is FIXED on 
using 5 minutes for idle times. 5 minutes is a SHOULD, not a MUST and 
for a client to DEPEND on a SERVER using 5 minutes is short-sighted 
engineering.
This should be done using an SMTP extension where a server can expose 
server timeouts perhaps and willingness to allow a client to sit idle 
redundantly and repeatedly.
Whats surreal about this, is the constant conflict of people ramming 
specs in people's spec yet have this strange tolerance for allowing 
and accommodating failure.  Very odd.   That doesn't work very well, 
IMEO, and if you wish to call that a "singular interpretation" thats 
fine by me.
As this particular case shown, the ignorance of the failure would of 
delivered bad messages and also delivered duplicated bad messages.
--
Sincerely

Hector Santos
http://www.santronics.com