Backup Mail Server Questions

Chuck Swiger cswiger at
Sun Sep 26 12:28:53 PDT 2004

Eric Crist wrote:
[ ... ]
> One of my friends needs backup DNS/Mail in the even their connection 
> goes down.  How do I go about setting it up so that his user base (about 
> 80 users) will not see any problems in mail transmission and reception 
> if their primary servers go offline.  I would like mine to automatically 
> pickup the slack.

Setting up redundant DNS is trivial: DNS is designed to do that.

Setting up a backup MX is easy.  It helps a lot if both mailservers are 
configured the same, and it is important that they have near-identical 
anti-spam and virus-filtering technologies.

Setting up a truly redundant POP/IMAP reader box is extremely hard.

To solve this problem for a local network, one normally uses a shared NAS box: 
in your case, this effectively requires one to set up a network-distributed 
filesystem, or some near-equivalent: for instance, a parallel database for 
mail stroage would serve as well.  All sorts of nasty issues-- like the 
security of the data going between the two fileservers, or DBs, or whatever; 
significant added latency due to the storage mechanism confirming updates have 
propogated; etc appear.

My opinion is that it's better to go with a primary mail reader box and make 
very certain that box doesn't go down by using redundant hardware and a backup 
network link is easier and less likely to suffer from the "lets create a 
complex system with lots of moving parts which never gets fully tested and 
thus breaks in some weird way when the unexpected happens" syndrome.  :-)


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