Documentation of big "mail systems"?

[Vlad GALU]

On Tue, 12 Oct 2004 23:20:51 +0200, Stephane Bortzmeyer
<bortzmeyer at nic.fr> wrote:
> I'm currently writing a proposal for a webmail service for, say, 50
> 000 to 500 000 users. I'm looking for description of existing "big
> mail" systems, using technologies like scalemail
> (http://scalemail.sourceforge.net/), specially with an emphasis on the
> storage subsystem for the servers (my weak point, I don't really have
> enough experience with SAN, NAS, and so on).
> 
> Of course, with a FreeBSD (and free software) bias :-)
> 
> I do not need general advice (such as "Postfix rules, Exim sucks" or
> "Maildirs are faster") but actual description of existing and running
> systems. Googling seems inefficient for that purpose and I presume
> that many interesting papers are only in closed and paying conference
> proceedings :-(
> 
   I've been running a system with ~2,500,000 e-mail accounts for
about two years. It uses qmail and a specially crafted version of
vpopmail. We modified vpopmail so it uses the sqlrelay API instead of
the original one, so we could proxy all the database requests through
a single connection. The Maildirs are stored on another machine, with
fast fibrechannel disks. For POP/IMAP we use Courier-IMAP, which uses
vpopmail as a storage backend. The system is perfectly scalable. Our
number of users has known a very abrupt growth in the last 7-8 months,
but it behaved really nice. Database machines can be indefinitely
upgraded. Storage devices can be added. As a personal notice, disk I/O
would be more efficient with Postfix, but we chose vpopmail's
management flexibility instead. We extended its API and rewrote the
information it kept about every account (some user prefs among other
stuff). The relay machines use qmqp to relay mails in a round-robin
fashion to four machines that act as outgoing default gateways, thus
dramatically improving the performance on the storing machines. I
can't see this going down in less than 7-8 years.

P.S. the vpopmail backend is PostgreSQL.


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