Redundant Mail System Suggestions

[Johnny Stork]

I am working with a client seeking redundant mail and dns services so 
have been trying to come up with some suggested architectures.

client has dual internet connections. So my first thought was create two 
identical MS/MW (mailscanner/mailwatch) systems, and assign each a 
different MX record with one being higher priority than the other. The 
machine running MS/MW would also be a DNS server so what would be the 
best way to setup some redundancy for both DNS and incoming mail?

Primary MX Record 111.111.111.111 (Internet connection 1)
Secondary MX Record 222.222.222.222 (Internet connection 2)


What are the benefits/differences between creating a  single A record 
with the same hostname, but the two different IP's above, versus 
multiple MX records but all with the same/different priority? Or, just 
list the machines as seperate MX records with the same priority?


The next step is how to I ensure that the MS/MW systems on both servers 
remain synchronized? I can easily point them to a common Mysql database 
which will be running internally and will be redundant by way of a RH HA 
Cluster, but what about the mail user accounts? The client will be 
running an internal groupware solution, possibly Scalix, so all mail 
coming in to the gateway MS/MW servers will simple get forwarded with a 
mailertable entry so is there any need to synchronise anything else 
between the two gateway MW/MS servers?

If anyone has any other suggestions/ideas for setting up such an 
environment I would be greatful.




-- 
*Johnny Stork*
Business & Technology Consultant
stork at openenterprise.ca