High availability mail server options

[Guy Fraser]

On Tue, 2005-04-10 at 08:03 -0400, David Hollis wrote: 
> For my company, I've setup a mail/groupware environment that uses
> Postfix, OpenLDAP, Postgres, Apache, etc and am now looking at ways to
> make it a more redundant arrangement.  All of the components have
> methods to help me with the lone exception of the backend mail storage
> for the end users.  Ultimately, I am wanting to have systems at
> different geographic locations, not even on the same network, ideally
> with users able to access any of them at anytime and be able to do their
> thing.  The users mail storage is in Maildir format which seems like it
> will help any replication type scenario.   I can't just NFS mount the
> mail directories, because then my NFS server becomes my single point of
> failure.  Do things like GFS work to handle this?  If so, do they
> operate across slow links (not talking dial-up here, but general
> Internet cable/DSL type links)
> 
> If it helps, our total mail volume is not that tremendous so completely
> instantaneous replication isn't totally necessary, but I would want
> fairly quick convergence (say 30 minutes or less).
> 
The simplest way to do regional mail storage is to use internal sub-
domains, to route the mail to the regional end point.

Ex. 
user.name at domain.tld -> user.name at location.domain.tld

Where location.domain.tld points to the mail server where the mail is
stored for that user. Configure the end point mail servers to only
accept mail from the main mail server. I do something similar to this
for some of my customers, but I use the the mailertable feature in
sendmail. Do not list the end point mail servers in any MX records.

I have heard of mail servers that use information from LDAP to route
mail to regional mail servers, but have never looked for information
about them.