Re: [gentoo-user] [OT] opinions & know-how requested: how to create a mail cluster

[A. Khattri]

On Fri, 5 Aug 2005, daniel wrote:

> very cool.
> how many servers are you using for this?  do you have a rough ratio for
> users:servers?

Its hard to say what the ratio of users/servers is - we haven't hit any
major bottlenecks yet and we serve somewhere between 3000 - 4000 accounts.

We have two main MX servers. (We have a third one but its not ready to
join the team just yet).

One of those servers handles most IMAP/POP3/SMTP for customers.

A third server acts as a database server (it does a bunch of other
things not directly related to mail too). We have MySQL read and
write queries split between two database servers and vpopmail will happily
work that way. The "write" database server replicates to the "read"
database server.

Then there's the three spamd+clamav boxes.

So there's a total of 6 servers doing mail-related chores.

All of our mail servers are pretty beefy machines with Gb's of RAM and
SCSI disks. (Though the main POP3/IMAP/SMTP server also has hardware
RAID ;-)

The spamd+clamav boxes are super cheap (tiny boxes with IDE disks, <
$500 each), but they have the very fast CPUs since spamd/clamav is very
CPU intensive. They can scale linearly - when we feel we need it we just
add another filtering box. Just to give you an idea, we started with two
and after more than a year added a third filtering box.

If you're supporting < 100 people you probably dont need such an elaborate
setup though two MXers would be a smart move. (If you give them the same
MX priority in DNS, you'll get round-robin load balancing).

A neat feature of qmail is you can have your front-end MXers handle all
incoming/outgoing SMTP traffic (and maybe one spam/virus filter alongside
them), and then they can deliver to an internal "private" server where
people grab their email. This will spare your internal POP3/IMAP server
from handling lots of SMTP, spammers, virus storms, etc.


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