[Mailman-Users] How does the core of Mailman function?

Jon Carnes jonc at nc.rr.com
Thu Jan 23 18:36:09 CET 2003

Mailman is Open Source... so you can feel free to open up the hood (so
to speak) and take a look at how it works.

You can get Mailman to work a couple of ways, but the most common is to
simply let it make an smtp call to localhost and drop off the mail
similar to the way any email client would drop off a message to a

There are some differences (and I'm sure other folks will comment on
them), but that is basically it.  You can set Mailman to drop off each
message to each person individually (often refered to as VERP) thus
allowing personalization of messages, but by default Mailman will group
same domain messages together - up to 100 at one time (but

The Mailman/Qmail combo is very fast, as is the Mailman/Postfix combo. 
The local delivery is not even a bump on the road when it comes to
pushing messages out into the internet.  The main time constraints for
email movement are in the Mail zone (DNS) look ups and the handshakes
with various Mail servers around the Internet.

If you run a local caching DNS on the same box as Mailman and your MTA
then this helps a great deal. After that the next best improvement you
can make is to use an optimized MTA (like Qmail, Postfix, or Exim). An
optimized MTA re-queues slower servers to the rear of the line so that
the faster ones don't have to wait.  This means that 90% of your mail
flies out quickly and is not held hostage in a queue behind some
slow-assed server connections.

Alas poor Sendmail, it doesn't downgrade the slow connections so if a
few of the first servers it attempts to contact are dreadfully slow then
all the mail simply waits queued up until those servers are done. 
So what's the point of this ramble: The speed of dropping off your mail
to your local MTA is not going to effect the speed of the mailing list.
It doesn't matter how fast you slam your mail's into line, they still
have to wait for the MTA to push them across the internet.  So the best
you can do is get an optimized MTA.

Best wishes - Jon Carnes

On Thu, 2003-01-23 at 11:51, Jonathan Chum wrote:
> I'm interested on how Mailman is able to deliver out emails rapidly. I'm
> curious on whether it opens a pipe to Sendmail or Qmail, injects the
> message, then closes the pipe after each message it delivers or does it
> write a file directly into a queue folder waiting to be sent...
> The reason I ask is that people say SMTP is faster than mailing via Qmail
> and that by opening/closing a pipe to Qmail, it adds more overhead. Also,
> you'll fill up disk space faster by queuing up messages than to directly
> email the message.
> I'm weighing down alternatives and method of mail delivery for a large
> client of ours.
> Regards,
> Jonathan Chum
> Systems Developer
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