[Mailman-Users] another question about invitation confirmation subject line/VERP

Brad Knowles brad at shub-internet.org
Wed Nov 28 05:18:18 CET 2007

On 11/27/07, Christopher Adams wrote:

>  One concern - Charles mentioned how 'expensive' it was to use VERP
>  with Postfix. I am wondering what kind of hit on the responsiveness of
>  my Mailman server will be.

There has been some research on this topic, which is summarized at 

>                              I have over 500 lists and 250,000
>  subscribers.

That would be one of the larger mailing lists known to be running 
Mailman, see 

>                If VERP being used for Mailman causes more mail activity,
>  could this result in slowness of list message delivery?

Well, it all comes down to how much activity your lists have.  A list 
that has hundreds of thousands of subscribers but which only gets one 
post per month is not necessarily going to see the same sets of 
performance problems as a site that has a smaller number of lists 
with a smaller number of recipients, but where the lists are very 

For that second URL shown above, contrast the profiles of 
HostMySite.com and panic.com as compared to lists.apple.com and 

Going back to that first URL shown above, I think the most critical 
summary paragraphs are these:

   The network penalty between SMTP_MAX = 1 (effectively VERP) and any
   kind of batching (SMTP > 1) is roughly 50%. To get VERP or customized
   footers or customized anything, you double your network bandwidth.

   There is very little advantage to setting SMTP_MAX > 5, UNLESS your
   subscriber base is heavily stratified onto very few sites. If you
   have really large groups of subscribers on AOL or Hotmail, it can help
   cut network bandwidth, but at best, it seems to be about a 10%

Keep in mind that this is for the test set described, but we believe 
that this is a reasonably accurate description of many Mailman 
mailing list servers & services.

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

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