From: Jorey Bump (listjoreybump.com)
Date: Wed May 02 2007 - 11:43:15 CDT

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Noel Jones wrote:

> Given your master.cf entry:
>
>> smtp inet n - n - 20 smtpd
>> -o smtpd_proxy_filter=127.0.0.1:10025
>> -o smtpd_client_connection_count_limit=10
>
> The above specifies that there will be no more than 20 smtpd processes
> running, and a single client can make no more than 10 connections at a
> time.
>
> Specifying a smtpd_client_connection_count_limit less than the total
> available (20) prevents a single client from using up all available
> slots - this is good.
>
> A per-client limit of 15 is probably a reasonable setting for low to mid
> volume servers. Note that client that hit the "connection count
> exceeded" error may experience significant mail delays, so keep an eye
> on things.

Thanks, Noel. I've changed the setting to 15 and will monitor it. The
server in question only supports the department's various mailing lists
and a small handful of low volume support addresses. The connection
limit is encountered only when the destination servers are trying to
return bounces due to unknown users (unfortunately, I don't manage the
mailing list with the problematic number of bad addresses, but have been
working with its administrators to try to minimize the damage). As such,
significant delays to those clients will merely delay bounces, so it's
not the end of the world. Still, I want to be as nice to them as I can,
since we're the cause of the problem.

I think I may also be able to get some mileage out of redirecting the
clients that are within our organization to another listener that
doesn't use the spampd proxy filter. This should improve throughput from
those sources considerably.

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