[Mailman-Users] MTAs

[Heather Madrone]

Thanks for your detailed answer, Brad.  I appreciate your
opinion on this subject.  If Postfix will do a better job than
exim, I don't mind switching at all.

At 10:08 PM +0100 3/25/05, Brad Knowles wrote:
>	In terms of providing good support for UltraSPARC, Solaris is
>going to be best, and I believe that Solaris 10 is freely available
>from Sun.  But that's not what I would consider an "open source"
>operating system.

That's our fallback plan.

>	In terms of Open Source operating systems for UltraSPARC,
>NetBSD is probably going to be the best, with OpenBSD close behind
>(they split off from NetBSD not too long ago), and FreeBSD catching
>up very quickly.  There may be some Linux distributions which also
>support UltraSPARC, and they might have been decent in the past, but
>I think they're tending to drop it in the same way that Debian has
>done.

FreeBSD works great if you don't need a keyboard, a mouse, or a monitor.
Not an insurmountable problem for a server, but the FreeBSD hardware
support of the sparcs is a lot spottier than NetBSD or OpenBSD.  The
guy who started OpenBSD was responsible for the sparc ports for
NetBSD.

>> My previous service provider used postfix, and we had recurrent problems
>> with Mailman's queues getting silently hung up.  A friend of mine who
>> runs a Mailman/postfix site also has the same problem.
>
>	Hung up?  In what way?

All mailing lists on the server silently stop sending posts.  No errors in the
logs, no console messages, no nothing.  Qrunners still appear to be
functioning normally.  A mail loopback test diagnoses the problem and
restarting Mailman clears it.

As I said, I haven't been able to see this problem since I started running
my own server.  It was happening at least once a week before that.

>> 	* Exim's ability to handle VERP processing through the MTA
>> 	rather than having Mailman have to do it.
>
>	Postfix has support for XVERP, and there have been patches
>posted which allow Mailman to take advantage of that.  I don't
>personally like that option, as I don't think it really saves you
>anything, and it certainly takes a lot of the control away from
>Mailman that I would normally want to maintain.  But if you want
>this, you can do it with postfix.

With exim, trying to do VERP processing on the digest runs caused Mailman
to flood exim, even when I turned the number of sessions and connections
way down.  It also brought my poor Mac, which was not meant to be a server,
to its knees.  I'm hoping that the sparc will be able to handle peak loads more
gracefully than a Powerbook.

One of the reasons that I'm considering Postfix is that I wonder whether
it might be more efficient than exim.  I have a hunch that exim might do
more work than it needs to to get the job done.

>> 	* Exim's fine degree of control of transient and permanent
>> 	delivery errors (by host, by address, by error type).
>
>	I'm not sure I understand what you're talking about.  Can you
>be more specific?  I know that postfix gives you a lot of control in
>these areas, but without knowing more about how Exim does them, it's
>hard to compare.

It's described in excruciating detail in section 32 of the exim specification.

	http://www.exim.org/exim-html-4.50/doc/html/spec.html

Basically, you can have a set of retry rules that go like this:

	host (or regexp)	error (or regexp)	retry strategy

	the.host.name  rcpt_452   F,1h,10m
	*                      quota	F,4d,6h
	*                      *		F,2h,20m; G,16h,1h,1.5; F,4d,6h

The first rule tells exim to retry rcpt_452 errors for host the.host.name every
ten minutes for an hour and then fail.  The second tells exim to retry all quota
overruns every six hours for four days.  The third rule says that all other errors
should be retried every 20 minutes for two hours, then at increasingly longer intervals
for the next 14 hours, then every six hours until 4 days have elapsed.

Okay, so it's not simple.  Easy enough to figure out, though, and it does give
you the ability to tune exim to deal with the kinds of errors that you run into.
It pains me to see endless retries of errors that aren't going to go away in minutes.

>> 	* Ease of configuration and administration.
>
>	Postfix is the only MTA on the planet that can have a truly
>useful two-line configuration file.  Moreover, it has the most
>intelligible configuration file that I have ever seen.  Better
>still, it comes up "default secure", unlike every other MTA I've
>ever seen.
>
>	I've seen Exim configuration files, and it's hard to tell
>what goes where, what is a router versus all the other ways that
>certain things could be handled, etc....

As I said, I've never tried Postfix, so my only point of comparison is
sendmail.  I am fairly confident that any MTA would look simple and
friendly next to sendmail.

>	When looking at Exim and Mailman, there is a distinct issue
>that has to be kept in mind.  The instructions for integrating
>Mailman 2.0.x are oriented exclusively towards Exim 3.x, and the
>instructions for integrating Mailman 2.1.x are oriented exclusively
>towards Exim 4.x.  If you've got Exim 3.x and you want to use
>Mailman 2.1.x, you're screwed.

Fortunately, the documentation makes that abundantly clear. 

>> 	* Reliability.
>
>	All I can say is that the largest Mailman installations in
>the world (that I know of) exclusively use postfix.  You'd have to
>ask them why they went this route, but my personal belief is that
>postfix is more powerful, flexible, and scalable than Exim, or most
>anything else available.

How would you rate Postfix's efficiency?  Is it fast?  Does it limit
network traffic to the necessary and keep its disk reads and writes
down to a dull roar?

Bandwidth is a consideration, since this will all be flowing on a fairly
slow DSL line (speed in this case limited by geography).

>> What are some reasons that I would consider postfix instead of exim?
>
>	Well, for a small site, it mostly comes down to personal
>preference.  Regardless of whether I think that postfix is
>head-and-shoulders above Exim or not, if you're familiar with Exim
>and you feel comfortable administering it, then you should seriously
>consider continuing to go that route.  Of course, your hosting
>provider might also fit into this picture -- if they're not familiar
>with Exim, then if you have any problems you may not be able to rely
>on their help.

My ISP is just doing bandwidth and DNS entries, so they don't enter
into the picture at all.  At this point, I'm my own service provider.

>	We use postfix on python.org for mailman-users and the other
>mailing lists we host, the freebsd.org folks use it for their mail
>servers, and lists.apple.com use it for theirs.  However, just
>because we use postfix does not necessarily mean that you have to.

Do you know why the choice was made to use Postfix on any of those
sites?  

-- 
Heather Madrone  (heather at madrone.com)  http://www.madrone.com

A rolling stone gathers no mass.