IAMP servers in FreeBSD for ISP

[Brian Candler]

On Fri, Jul 07, 2006 at 12:00:17AM -0300, User Freebsd wrote:
> >Anyone care to share what IMAP servers they have found to scale best?
> 
> By far, IMHO, the best is cyrus-imapd ... it was originally developed by 
> Carnegie-Mellon University to handle their on campus email, and grew 
> quickly out of that ...
> 
> If I recall your environment at all, one nice feature of it is that it 
> supports something called MURDER, which, effectively, is a way of having 
> your mailboxes literally spread out over multiple backend servers ... 
> all the mail comes in through ServerA, but, as an example, mailboxes a-m 
> get stored on ServerB, and n-z go to ServerC ...
> 
> They've also just recently added a replication ability, so that you can 
> have backup servers ... ServerD is a backup of ServerB, ServerE is a 
> backup of ServerC ...
> 
> The thing is, it would most likely eliminate, or greatly reduce, your NFS 
> requirements ...

Conversely, it also means that it is not safe to use with NFS backends. So
if you already have a good and/or expensive NFS appliance, you won't want to
use Cyrus.

Remember that Courier has a proxy front-end built in, so you can use a proxy
cluster instead of an NFS cluster (or even have some accounts on Courier and
proxy others to Cyrus; a very nice migration tool)

If you do want to go the Cyrus route, there are some good papers from
Cambridge University in the UK describing their setup:

http://www-uxsup.csx.cam.ac.uk/~fanf2/hermes/doc/talks/2004-02-ukuug/
http://www-uxsup.csx.cam.ac.uk/~fanf2/hermes/doc/talks/2005-02-eximconf/

Actually I have very good experience of courier-imap + exim in a large ISP
environment, but the vast majority of users were POP3, not IMAP. Also,
although Courier's sqwebmail has a not particularly pretty interface, it
*does* perform very well under heavy usage (I suspect much better than a
PHP->IMAP solution) since it accesses the Maildirs directly.

Regards,

Brian.