There are two parts to this: SMTP replication and mailbox replication.
SMTP replication (rather, failover) is trivial, and most people should
already have this setup with MX records and multiple smtp relays where the
secondary servers just forward to the primary servers and queue mail when
the primary is down.
Mailbox replication is somewhat harder, but can still be done I think. One
approach might be to try using Coda to replicate a filesystem across
several servers with multiple mailbox servers (imap,pop) and local
delivery on multiple machines. I'm not sure though if Coda is really
stable enough to do this, and whether the distributed locking mechanisms
will work well enough without significant changes to the delivery agents
and mailbox software. When I last looked at Coda, it seemed to have plan
of making copies and trying to merge changes back together, which might
mean is doesnt' really implement distributed filesystem locks the way DFS
or even NFS lockd does.
Alternately, one might create a multimaster replication protocol for the
mailbox software, similar to Oracle multimaster replication. This might
also be done using Oracle as the backing store for the mailbox software.
Its an interesting project.
Replacements for exchange scheduling and calendaring can be found by
searches for RFC2445. Check out www.calsch.org/icalsite.html, which lists
some open source implementations and other useful info.
--Dean
On Fri, 12 Apr 2002, Betsy Schwartz wrote:
> I recently interviewed at a software-related company with 4-500 employees,
> mostly in a central location but with a dozen small satellite offices
> around the globe. They currently have a single centralized mail server
> running Sendmail/POP behind a firewall and I believe a VPN also.
>
> The IT manager is interested in email *replication*. In her ideal system,
> if the mail server goes down, people would be able to get their mail from
> an alternate location. She'd also like to see the foreign offices get their
> mail locally. And, she's also investigating Exchange server to allow mail
> and calendar functions to combine (they are currently using Meeting Maker
> which sucks in a number of ways.) So, both of my questions involve
> designing a new mail server infrastructure.
>
> First, what if anything allows for true mail replication? It's simple
> enough to set up satellite servers and sort mail to different locations,
> but I am not aware of anything that will let two or more mail servers stay
> *synchronized* with each other. Searching on the Net only gets me Lotus
> Notes links, and I don't see anything remotely like this on the Sendmail or
> Postfix sites. I am also wondering how this could work without being a huge
> load on the network - if it exists, if it is feasible outside of a tightly
> linked local cluster? Just using a highly redundant local machine would
> increase mail uptime but not be much good in the event of a network outage.
> Are there any solutions, and if so are there any that make sense for a shop
> of this size?
>
> Second, is there a good, accessible from multiple platforms, alternative to
> Exchange that will handle mail and calendar? I'm not so familiar with
> calendar software but would hate to move to the Microsoft mail model. I'm
> happy to agree that Meeting Maker sucks but are there any real
> Exchange-busters out there?
>
> Should these people really be running Lotus Notes? Domino Server seems to
> do a lot of what they want...
>
> thanks
> Betsy
>
>
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