[OT] Which one is best MTA for me?

LI Xin delphij at delphij.net
Tue Aug 28 19:29:15 PDT 2007

Byung-Hee HWANG wrote:
> Hi,
> Recently I am considering to move to another MTA. At one time I was
> wondering what mail server big ISP are running. I can't decide postfix
> or qmail. 
> Which one is best MTA for me?

We (one of the largest ICP company in China and provides some billions
of free e-mail accounts) has replaced our locally hacked qmail with
postfix in 2005.  I and one of our sys-op has accomplished all of the
necessary migration work (coding to re-implement our features, testing,
and migration itself) within three weeks, so once you have confirmed
what your requirement is, it's not very hard to do.

I do not want to say simply that you will want postfix, but I would like
to explain the reasons why we have did the migration:

 - Performance.
qmail uses about 3 times of file I/O operation for each mail delivery,
compared with postfix.  For a busy MX server this means that you have to
prepare more servers to do the same job.

 - Features.
Most of extension to qmail has to be done by patching.  It's true that
there is a lot of qmail patches floating around, but you have to
carefully maintain a local qmail tree.  Postfix has a lot of built-in
anti-spam and other features, and it is relatively easy to implement new
feature with Python/Twisted through Postfix's interface - no patch
needed for postfix itself.

 - Manageability.
Our system administration team used to be very familiar with qmail.
However, for large ISP/ICPs, qmail fails to solve the following
essential problems that postfix does not have:
  - Hard to reconstruct mail queue after damage
    In postfix this can be done with 'postfix check'.
  - Have to watch its queue situation
    Once you got the queue stuck with a lot (200,000+) e-mails that can
not be delivered temporarily, e.g. due to a backend hardware issue, all
e-mails would be delivered very slowly, and incoming e-mail would make
the situation worse.  We used to have a monitoring script that adds an
ipfw rule to block all subsequent incoming mail to work around this
issue.  With postfix, stuck e-mails are stored in separate queue.
   - and a lot more...

 - Maintainability.
Extending postfix for your own need is easy, our new anti-spam system is
primarily written as a policy/filtering/table lookup daemon with
Python/Twisted, making the code much more easy to understand and
maintain.  It's not easy for someone to be able to pick up the qmail
patch due to the coding style and lack of comments.  More importantly,
postfix is being actively maintained, but qmail is not.

I'm not sure about the problem you are having.  If you are going to set
up a new mail server (cluster) then don't use qmail, it would be a
nightmare if your system grows.  Postfix is a good choice, and there are
some other choices, e.g. sendmail, exim, etc.

Xin LI <delphij at delphij.net>	http://www.delphij.net/
FreeBSD - The Power to Serve!

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