Re: IAMP servers in FreeBSD for ISP

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.
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