[Exim] Exim Testimonial from Gambling.com

Hi Nils,

Here's what Gambling.com has to say about Exim.

RELIABILITY
===========

The primary mail gateway for our domain (and a handful of virtual
domains as well) runs Exim.

The server handles mail for about 50 staff, and as such is not that
interesting an advertisement, except that in its 18 months of service,
not a single "lost mail" complaint that we've investigated has proven
that our mail server lost a message; it always comes down to someone
else's network provider.

The best feature of Exim, and the one that made me deploy Exim instead
of qmail (which I was told was faster) is its logging. As an operator,
the ability to find out where a message is in its lifetime, why it
hasn't been delivered yet or why it failed to be delivered is a breath
of fresh air.

FLEXIBILITY
===========

Our environment demands an incredibly flexible mailer, which Exim has
proved itself to be.

For a start, we use exiscan and Sophos Anti-Virus to block messages with
viral content. We've also configured Exim to reject fragmented
messages, that could otherwise be used to "slip viruses through" the
virus scanner.

Then we have a complex set of interception rules, including interception
of all mail from the development server, ensuring that our developers
don't accidentally spam hundreds of thousands of site guests. We also
have "pass-on interception" rules in place, that allow us to receive
copies of messages matching certain criteria (e.g. from an ex-employee,
from an insecure web form etc.).

Of course, our staff use a mix of POP3 and IMAP to retrieve mail, and
some users require mail forwarding as well. Exim cruises through this,
handling various kinds of mailbox formats well.

And of course, access control is incredibly powerful. Exim's lookups
allow the operator to limit access in just about any way imaginable,
whether it's based on a database, a DNS blacklist, an LDAP server,
NIS, a flat file on disk, PAM, and more. These things can be used in
combination.

As an example, we protect ourselves from relay abuse by only allowing
relay from IP addresses from which successful POP3 authentication
has been received in the last hour. This was simple to set
up, requiring only a PostgreSQL database lookup on a "POP-before-SMTP"
database that gets updated by scripts that watch the POP3 server's log
files. Of course, we could have used MySQL if we preferred. If we'd
needed to use an MS SQL database, we could have used Exim's embedded
Perl feature with Perl's DBD::Sybase driver!

PERFORMANCE
===========

Our mass mail server handles comminication with our site guests and is
required to send large volumes of mail in very little time.

The hardware is beefy (dual P3, 1GB RAM, IBM 15Krpm drives on a Mylex
eXtremeRAID 2000 controller), but the performance is astounding.

We pregenerate queues of 300,000 to 500,000 unique messages (9KB - 35KB
in size), which takes 20 to 40 minutes. This is slow because generation
of mail involves database activity -- Exim is not the bottleneck here.

Once mail for a day is queued, we send out mail faster than any other
server I've encountered -- between 120Kmph (thousand messages per hour)
to 240Kmph peak rate, averaging around 130Kmph and finishing up within
2.5 hours. Keep in mind that this includes delivery to a significant
number of Hotmail recipients, and Hotmail's gateway hosts have terrible
availability problems.

This required some fine-tuning, and involves running about 400 queue
runners simultaneously, with a separate queue for Hotmail. But then
Unix-like operating systems are built to handle load, and our Unix-like
flavour (FreeBSD) copes admirably.

Given that our members represent such a broad cross-section of mail
domains, these delivery rates are impressive. It's a good thing we're
as well connected as we are, because it's not uncommon for our mailshots
to sustain rates of 18Mbps at times. :-)

CONCLUSION
==========

I believe that qmail (and possibly Postfix) may be faster than Exim in
certain configurations. However, it's safe to say that Exim is one of
the top 3 mailers in the world, and for applications requiring high
performance, no-nonsense reliability and flexible configuration, Exim is
the mailer of choice.

All the best with your deployment. :-)

Ciao,
Sheldon.
--
Sheldon Hearn
UNIX Systems Manager - Gambling.com