How to configure redundant or backup (MX) mail servers


MailEnable can work as a backup MX mail server.


There are two principal ways to configure redundancy with MailEnable.

The simplest way to achieve redundancy is to install a copy of MailEnable as the master server. You can then install separate copies of MailEnable on other servers and smart host the domains to the IP address of the master server. This will mean that if the master server is down, that the auxiliary servers will accept mail for the domains and hold it until it is online.

The DNS/MX settings for the domains need to be changed to configure the appropriate MX preferences. Other mail servers learn about your mail server via DNS MX records. They are the means by which someone enumerates a target domain to the server responsible for receiving mail for that domain. MX records have a preference associated with them that determines the order that they are used. The lowest preference is attempted first. The lower the preference value, the higher the priority. Hence, an MX record with a preference of 1 would be attempted before an MX entry with a preference of 10.

Once the mail server is configured in accordance with this article, if the primary mail server is offline, the mail will be delivered to the backup MailEnable server (because it has the next MX preference). It will then be received and smart hosted back to the primary mail server, and will be retried in the MailEnable queues until it is either delivered or it exceeds the queued lifetime.

The abovementioned approach is used if backup mail servers are distributed in different geographic or logical locations.

A second alternative is to host all mail servers on the same local network and cluster the servers. This allows MailEnable to be installed on multiple servers and have them use the same store for their messages and post office data. Any of these servers can then be used to access the mail. It requires that one of the servers share the mail data and configuration directories and that the others access them.

The following articles explain this approach:

How to cluster MailEnable:

How to configure MailEnable web mail on a different server:


More info on DNS and MX records is available at:

Which DNS should be used?:

How to configure and host DNS infrastructure for MailEnable:

DNS Records to create when hosting mail domains:

Installing and configuring MailEnable:

Troubleshooting DNS MX Lookup Issues:

How to configure the infrastructure required to host a mail server:

Product:MailEnable (All Versions)
Class:HOWTO: Product Instructions
Revised:Wednesday, November 23, 2016