DNS offers a mechanism (MX Records) for specifying backup or alternate hosts for mail delivery. This mechanism also allows hosts to assume mail-handling responsibilities for other hosts that are not configured to accept mail, such as a null client. MX records also provide a mechanism of forcing all mail to go to the hub machine or mail server. MX records specify a mail exchanger for a domain name (i.e. a host that will process and/or forward mail for the specified hostname). As an example, this is done by adding entries into the DNS server as follows:
In the example, the server himalaya.sc.steeleye.com has an MX record that will cause mail for this server to be delivered to relay.steeleye.com. The server which is to be LifeKeeper protected should not have any MX records. The LifeKeeper protected alias IP address that is used during the Postfix resource hierarchy creation should be used for MX records instead.