>Does anyone know of any tools available that will allow someone to do
>"distributed" or "replicated" mail servers?
The short answer is "yes, but nothing really good".
I did an extensive search on this a year or so ago and came
up with the following conclusions.
Mechanism:
(1) Use Lotus Notes.
Pros:
replication works mostly transparently.
Cons:
their imap implementation, at least as of 5.x, sucks.
(VP of mktg tells us a year after they tried to sell it to
us "thank god you didn't buy our product. you'd have
been f*cked!").
proprietary commercial sw ($); limited platform support.
need lotus expertise to manage.
(2) Use Innosoft PMDF on an OpenVMS cluster.
Pros:
rock-solid VMS reliability.
excellent IMAP implementation and an awesome MTA to boot.
Cons:
product might be discontinued in a year or three since Sun bought
Innosoft.
need VMS expertise to manage, and need VMS hardware (compaq alphas).
In particular, configuring such that a cluster
transition won't lock up the shared disk takes
some thought. VMS market now stable, but almost certainly not
growing, making long-term support issues questionable.
(3) Various commercial high-availability systems, such as those
offered by qualix, veritas and others. (mostly targeted for solaris).
Pros:
sort of works.
Cons:
not true shared-mailstore access, much more of a warm-backup
level solution; you can't hit the same mailstore at the
same time from two different machines, you can only have
one machine grab and fsck the mailstore if the other machine
crashes. in general this approach is a kludge with some
gotchas to watch out for, and takes good sysadmins to
manage workably.
(4) Home-rolled high-availability.
In theory, one could use rsync or unison
http://www.cis.upenn.edu/~bcpierce/unison/
or some linux distributed filesystem
to replicate a mailstore back and forth between two machines
with similar cyrus or uwash imap configurations.
if one machine crashes, you start the server processes on the other
and reverse the direction of replication when before bringing the
first server back up.
Pros:
can use free sw and commodity hw.
sort of works.
Cons:
can get yourself into deep trouble with no help line to call.
still isn't really a shared mailstore; about as bad a kludge
as commercial high-availability for unix.
Note: someone just posted to the list about a successful use
of this approach using networked raid under linux in which
both servers get live access. progress marches on.
