How do I create a backup mail service?

[admin]

The first and most important thing you need to understand is how MX records work (please view How do I configure my MX records on my DNS?). The concept of a backup mail service is that one computer is the primary receiver of incoming mail and one or more other computers are backup receivers, which on receiving an email will attempt to forward it onto the primary server. If the primary server is off-line, a backup mail server should then hold all incoming mails for a given period, during which it should keep trying to forward the mails on.
To set up Ability Mail Server to act as a backup, you will need to create a new domain, which should be configured as a backup domain. You then need to create a static route for this domain. The static route should be set to relay mode and should direct the flow of mail back to the primary server. It is also recommended that you configure the static route to hold the mail for longer periods by setting a longer queue life. This ensures that the primary server has sufficient time to get back online.
Once Ability Mail Server is configured correctly, you can then specify the host / IP address as an additional (higher value priority) entry in the MX records for that domain. This will then ensure that if the primary server goes down, the backup server will then begin receiving the mails for that domain.