Two methods that can be used to create a redundant mail server
environment. Depending on what you are trying to accomplish one of the two
configurations outlined below will allow you to either set up your environment
so no mail is lost if any downtime occurs, or so mail throughput has no
downtime due to any server problems. Both of the configurations can be
implemented together so as to obtain the desired affects in one
The two approaches are:
1. Store Mail While Primary Server is Offline:
The article below, shows how to configure an MX record to
have a backup MX.
This will mean that if the primary mail server is
offline, that the secondary backup MX will accept the e-mail on behalf
of the primary.
To do this, configure the secondary
MX mail server with all the domains to host, and use the smart host option for
each domain, or in the SMTP service properties so that it is directed
to the primary MX mail server. This way, if the primary
goes offline, then the secondary will accept the mail, and queue it until the
primary server is back online. This method does not allow users to access or
send email, as the primary server is the only one with the authentication
details and the stored email.
2. Server High
For high availability MailEnable can run on two or
more servers in a mail cluster, where all servers connect to shared storage for
the configuration and email data. The software handles file locking so has the
advantage of allowing all servers to run mail services at the same time. This
can both allow load balancing and failover. This will also
require a clustered IP address for any clients and other servers to connect to.
There are many network load balancing switches available on the market that will
do this. The MailEnable
Enterprise Infrastructure Configuration Guide outlines this approach in
How to configure back up or redundant mail servers:
How to cluster MailEnable: