If the servers are not geographically separated, then you can do this
fairly easily by simply placing them behind some sort of
load-balancing/fail-over device (Foundry, Cisco Local Director, Linux
LVS director) and either load balance them or do active/passive
For the vpopmail database, if you're using MySQL, you can simply setup
MySQL replication, however changes made to the secondary will not
replicate back to the primary when it comes back up. For that you would
need to run a third MySQL server to act as the update server which then
replicates out to both clients. When the primary server came back online
you'd simply dump the database on the update server and import that into
the client and restart replication.
Email files are even easier since you can simply use nfs on a third
server, or look into a replicating file system like Coda or Intermezzo
(both are supported in the linux kernel, but I have no real experience
with either). If you deal in small volume of email, simply rsync'ing
when the primary comes back online would probably also work, and copy
the mysql database back over wouldn't be too much trouble either.
The final option, if you have no hardware to spare for this, to handle
smtp/imap/pop3 traffic failover would be to use some of the tools from
the Linux-HA project and use a virtual IP to actually receive outside
traffic on, and have that migrate to the unfailed server in the event of
a failure.
I've got a configuration similar to the first suggestion, and have built
redundant pairs of machines using the second configuration, so let me
know if you have any more specific questions regarding these sorts of
On Fri, 2003-07-25 at 05:22, Rudi wrote:

> I've also got a question on this topic:
> If I have a primary, and a backup mailserver, and the primary goes off, how
> do I automatically redirect clients to the backup mailserver? And how does
> one keep the username /password database synced? The other question is, what
> happens when the primary comes back online again? How do clients get their
> email from the backup server? Do I manually have to copy all the mail onto
> the primary server again?
> --
> Kind Regards
> Rudi Ahlers
> Tradeleads IT Director
> +27 (82) 926 1689

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