Lansing, Dan writes:
> I am setting up a backup for my mail server and would like to keep it
> synchronized with the main one.

Your best bet here with a normal mail system (qmail, Postfix, etc.) is to
store mail using NFS on a system that has RAID.  Backups don't work well for
mail, since they will always be out of date.  I don't know of any network
replicated file systems for free operating systems.

If you need multiple front end servers (doubtful, since the disk is always
the bottleneck), use a SQL database to store your user database.  MySQL is
good for this since it is fast and has reliable replication.  vpopmail, a
popular virtual domain manager for qmail, works well with MySQL.  You can
also setup Postfix to use MySQL for the user database.  Even if you don't
need multiple front end servers, storing your user database in a SQL
database is nice.

An alternate approach is PowerMail.  It is designed to be redundant and
distributed.  It allows you to run storage daemons on multiple machines that
are all kept in sync automatically.  The user database can be stored in
MySQL, which allows for MySQL replication.  I like the concept, but would
need to do testing before I put it into production.  I was discouraged by
the fact that it didn't compile "out of the box" on FreeBSD.  Commercial
support is available from PowerDNS, the company that wrote it.

http://www.powerdns.com/products/powermail/

Another approach is to store both your user database and mail in an SQL
database.  The allows you to use MySQL replication to automatically
replicate everything.  To my knowledge, dbmail is the only open source mail
server that does this.  I have never tried this software, but I like the
concept.

http://www.dbmail.org/

-- 
David Phillips <david at acz.org>
http://david.acz.org/


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