High Availability E-Mail Solution? Seeking Recommendations

[Tim Post <tim.post@netkinetics.net>]

Hello to all on the list :)

I'm looking for a high availability e-mail solution that would suit a
single (or several) domains easily deployed across a farm of 5 or 6
identical servers. 

I've tried the following things :

1 - exim/qmail on a single system image (Open SSI with CVIP/LVS using
weighted direct routing, and also tried a less elaborate ocfs2 setup)

2 - basics (multiple mx's with fetchmail keeping inboxes centralized)

I'm not really overjoyed with either solution because they are intricate
to deploy and document so others can maintain them.

I find myself still looking for a better solution because I am hoping to
find something a little easier.

My ideal setup would be something open source, using a database backend.
Its rather easy to deploy HA database clusters, and using something like
Xen its also rather easy to split a DB cluster for multiple (yet
isolated) uses.

I have some domains that have been getting literally clobbered by pump
and dump stock spam and even with using RBL's / DNSBL's the activity is
still leaving their MX sluggish or unavailable a few times a day. Rather
than continuing to fight a losing battle of blocking and filtering ..
I'd rather just beef up email services to handle it.

If you had 3 - 5 dual core opterons, all having a public (10/100) and
private (gig-e) nic [ private being connected to an isolated gig
switch ] that you could devote to trying to make an 'armored' MX
cluster.. what would you use? 

Thank you in advance for any thoughts or recommendations. Google is
turning up mostly junk article wikis on the topic (big surprise).

Best,
-Tim