Qmail Support Forum

admin · Site Admin Joined: 21 Jun 2005 Posts: 209

Hi, everyone. I e-mailed this list about a week ago, asking for help
with my mail server, which was unable to delivery mail to many list
subscribers because the ISPs were limiting the number of connections I
could make per minute. Since qmail puts each message into its own SMTP
connection, and at two of my lists had 50 messages/day and 1,000
subscribers, I was hitting a wall.

I received a lot of good suggestions from this list. In particular,
Jeremy Eder wrote:
> Sadly, most everyone with a busy server has run into this.
> I've gone the 'contact recipient isp, beg for whitelisting' thing, and
> got nowhere.
> Take a look at the url and posts below, we had a talk about this a
> while back.
> I haven't had a chance to test Richard's code, but if you do please
> let us know as I believe it will benefit all.
>
> http://marc.theaimsgroup.com/?l=qmail&w=2&r=1&s=control+delivery+rate&q=b
I tried the code posted in the above thread, and it seemed to make
things worse; my CPU usage went through the roof, and delivery success
became more variable -- sometimes working well, but often getting stuck
even more than before. I fiddled with the configuration quite a bit,
but nothing changed the feeling that I got of doing a busy wait, with
qmail-remote trying (and failing) repeatedly to lock the
rate-controlling file.

Several people also suggested delivering mail to a local Maildir instead
of the problematic domains, and then using serialmail to deliver mail
from those directories on a regular basis. Maybe it's just me, but this
sounded like it would be hard to do.

I also received some advice on how I could use netfilter to send from
several IP addresses. Unfortunately, my hosting provider doesn't offer
the netfilter modules that I would need.

Establishing a second mail server would normally be a good idea, I
think, except that this is all supposed to be a fun, volunteer thing,
and I didn't want to spend money on another server.

Erwin Hoffmann wrote:
> In fact, this is based on qmail's send-one-message-then-quit strategy for
> sending emails. Postfix, for instances, bundles all requist for a
> receipient domain and sends them in one go.
This got me thinking: If the problem is the number of SMTP connections
that I'm making, rather than the number of messages, and if the most
popular ISPs are the ones that are giving me trouble, then perhaps I
would be wise to switch to Postfix. So I decided to give it a shot,
keeping my qmail configuration intact -- and I must say that the results
are overwhelming and dramatic. Since installing Postfix yesterday, I
have literally no messages waiting in the queue, despite the same
traffic patterns as I had using qmail. Memory usage is way down, CPU
usage is way down, and people are getting their messages within
seconds. Configuration and installation was pretty quick and easy, as
well; I went from knowing nothing about Postfix to having it working
within about 36 hours, with the actual time invested being much less
than that.

My impression is that qmail might indeed be faster and/or more efficient
in a world where ISPs accept unlimited connections, or in which members
of a mailing list are spread across many different ISPs. But on a list
where members are concentrated in a small number of ISPs, and when those
ISPs limit the number of connections, the Postfix approach seems to be
better.

Thanks to those who responded for being so helpful!

Reuven