Re: [Exim] large scale exim/mail system

Hi Phillipp,

On Thu, 8 Mar 2001, Philipp Gimm wrote:

> to get back to topic:
> I'm completly lost with the Hardware thingy... (ever talked to a salesman,
> asking for some sort of advice from that company, and all he comes up with
> is "no problem, Sun Server, Storage System, Giga-everything. ...hrm, lets
> say 8.000.000 US$. when do you want to sign?") grrrr.....

I administer a system which has done up to 1.2 million emails a day (not
spam :-)). It is running on PC hardware with slackware Linux. I have
played with the kernel some to allow exim a better running environment -
4000 simultaneous hard limit of processes, lots of open files - you know.

There is some other black magic behind it:

* Extensive tweaking of the configuration file.

The Exim documentation is your friend. Read it... again and again and
again! Play with a setup, then see if you can make it faster.

* Hardware to suit mail dispatch.

Exim is not particularly computationally expensive. It's a good idea to
know your operating system though. Linux for example will build a large
file system cache. Looking at the primary box now, it is around about
340MB in size. Nonetheless, you need to have fast disk. I am using U160
SCSI. The mail spool has its own disk so as to take advantage of the SCSI
configuration.

It is a dual CPU machine - but this is overkill really.

I have 1GB of memory.

* Seperate services

You need to run the pop server on a different machine. Make sure that the
MTA is not writing to an NFS box - this is very slow, esp. under
Linux. This can cause problems if you want to do clustering and failover -
my example is used only for dispatch.

* Lookups

Use Berkeley DB, not mysql, not pgsql, not sql. SQL is slow. You can
easily plug applications into berkeley DB using the API - available for C,
perl etc.

Make sure you have a fast DNS near by. Setting up a DNS cache on the same
machine will not hurt it.

* Batch delivery

See the manual. Its just good.

There is plenty more that I could add. Perhaps Exim needs a 'build a fat
mail server' howto? It is a popular discussion topic from time to time.

Thanks

Gavin Sherry
Alcove Systems Engineering