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RE: FWIW Connection Sharing Stats

2011-08-29 14:19:33
I don't think one can tell whether a particular client is connection caching by 
observing protocol activity in terms of time between commands/disconnect.  I 
also don't think one can tell based on those same data whether any delays are 
caused by deliberate software action, CPU scheduling, network latency, or 
anything else.  I might make that conclusion if I saw a client sending periodic 
RSET or NOOP commands, but I haven't seen any evidence of such.

If someone thinks (for example) that Facebook might be connection caching and 
wants to find out for sure, one could always go and ask them.

I also have my doubts that the bad guys are implementing connection caching.  
Spammers have such enormous compute and network power at their disposal (when 
using botnets, at least) that they are probably not thinking too much about 
efficiency in terms of establishing new connections, which only adds complexity 
and makes their code bigger.  And, as far as I'm aware, bots typically try to 
do direct connections rather than relaying, and they tend to carry their own 
MTAs and even TCP stacks with them to avoid detection.  That means they're not 
using the open source MTAs that tend to implement connection caching, so those 
connections that do show some idle time are probably not the bad guys.

So, so far, I haven't seen anything that warrants consideration in terms of 
updating a standard.  I suggest that there are way too many assumptions being 
made about the data to warrant much action from the IETF, even something 

This is starting to sound like a conversation the ASRG might enjoy rather than 
this forum.

From: owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org 
[mailto:owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of Keith Moore
Sent: Saturday, August 27, 2011 7:31 AM
To: Keith Moore
Cc: Hector Santos; ietf-smtp(_at_)imc(_dot_)org
Subject: Re: FWIW Connection Sharing Stats

On Aug 27, 2011, at 9:53 AM, Keith Moore wrote:

On Aug 26, 2011, at 8:18 PM, Hector Santos wrote:

Among the spammers rejected with delays, many do try a new transaction with the 
same failed result.  Is this CS client behavior? I seems to appear that way.

Maybe the spammers are trying to deal with greylisting?

For that matter, I wonder if legitimate senders are trying to deal with 
greylisting also.  Maybe there are poor implementations of greylisting that 
block legitimate traffic too often.  Maybe there are some large-volume senders 
that don't want to deal with having greylisted mail in their queues any longer 
than necessary.  If retrying after a few seconds works on some greylists, it's 
not surprising that some senders would start doing it.