I actually just set the MaxAcknowledgementDelay to 1 and TarpitInterval to 0 on our internal relay connector.  I'll be sending a 60k + mailing today, so I'll see how it goes.

Thanks!

-----Original Message-----
From: LISTSERV site administrators' forum [mailto:[log in to unmask]] On Behalf Of Sparks, Michael
Sent: Tuesday, February 12, 2013 1:03 PM
To: [log in to unmask]
Subject: Re: Strange Delivery Delays

Another possibility: tarpitting or throttling on the SMTP host. Be sure your LISTSERV's IP has been exempted from anti-spam measures like that on your SMTP host.

On Feb 11, 2013, at 3:37 PM, Valdis Kletnieks <[log in to unmask]> wrote:

> On Mon, 11 Feb 2013 15:17:07 -0500, Liam Kelly said:
> 
>> As to why your SMTP server is taking so long, you'll need to run it 
>> down from that end.  Some of the usual causes are things like 
>> inefficient anti-virus and/or spam scanning of every message (my 
>> first guess), a disk I/O bottleneck on the mail spool disk, inbound 
>> mail throttling, or inefficient directory lookups for addresses to 
>> route locally.  Whatever the case may be, you aren't going to be able 
>> to figure it out by looking only at LISTSERV's end of things.  You need to go to the mail server.
> 
> Even today in 2013, an amazing percent of SMTP servers have broken DNS 
> setups that cause a lot of waits for DNS lookup timeouts.  Just a thought...
> 

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