[Mailman-Users] Rewriting or identifying late bounces

Brad Knowles brad at shub-internet.org
Thu Jul 9 07:08:09 CEST 2009

on 7/8/09 6:12 PM, Stefan Förster said:

> Thanks for your advice, Brad. The problem is that, due to policy
> reasons, outgoing mail has to pass a content filter, running locally
> on the Mailman box. With VERP...

Chuq von Rospach wrote some stuff in the FAQ detailing his experience 
with how VERP impacted performance on the systems he was managing.  Of 
course, this doesn't necessarily apply directly to your case, but it is 
instructive to read.

My recollection is that, in his case, he found that without VERP he got 
about two recipients per copy of each message transmitted -- due to the 
fact that some recipients are all on the same system and only one copy 
is sent to that system for multiple recipients, while others get unique 
copies because no one else is subscribed from that system.

That meant that enabling VERP roughly doubled the number of copies of 
messages that had to be sent (so that each person is guaranteed to get 
their own personal unique copy), but that this didn't actually affect 
the overall performance very much (since so much of e-mail is I/O bound 
and waiting for the system at the other end to respond).

However, enabling VERP also meant that it was now much, much easier for 
the system to automatically manage bounces (a.k.a., Non-Delivery 
Notices, or NDNs), delivery status notices (DSNs), etc....  This made 
overall management of the system much easier, and greatly reduced the 
amount of work that the system had to try to do to parse the bounces to 
try to figure out which recipient(s) it was in relation to.

If you throw a content scanning system into that mix, most of the 
content of each of those mailing list messages will be the same, so 
depending on how that content scanning system is configured, it 
shouldn't be that much more expensive to process 100 virtually identical 
messages as it is to process the first message in that group.

> I guess I will simply move the list server to another computer (and a
> different network).

OTOH, moving the mailing list function to a different server and 
separating that from the content scanning system is also a good idea, 
including lots of other reasons.

Good luck, and I hope that this works out for you.

Brad Knowles <brad at shub-internet.org>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>

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