My friend hosted their mail server in their own premises. Their in-house mail servers are connected to two fixed-IP Internet Connection. Since they have one one Mail Exchange server, setting up two MX records using the two different IP addresses might not help in this case.
| Round robin DNS is a technique of load distribution, load balancing, or fault-tolerance provisioning multiple, redundant Internet Protocol service hosts, e.g., Web servers, FTP servers, by managing the Domain Name System’s (DNS) responses to address requests from client computers according to an appropriate statistical model. In its simplest implementation Round-robin DNS works by responding to DNS requests not only with a single IP address, but a list of IP addresses of several servers that host identical services. The order in which IP addresses from the list are returned is the basis for the term round robin. With each DNS response, the IP address sequence in the list is permuted. Usually, basic IP clients attempt connections with the first address returned from a DNS query so that on different connection attempts clients would receive service from different providers, thus distributing the overall load among servers. More from Wiki! |
The key thing for a round-robin DNS is where loads are shared. The load are distributed among the first and second (or more) servers, randomly- without checking if any of them are down!
| When you sign up for the backup mail service, we automatically add our backup mail server in an MX record to your zone. This causes all incoming mail to attempt your primary server first, and if that fails, to try our backup server. When our backup server gets mail for you, it looks up your primary server, and periodically attempts to redeliver your mail to the primary. It will attempt redelivery for 10 days before returning the mail to the sender as undeliverable |
I do come across a MX backup features by Zoneedit. It has a workaround for this. It is a subscription based service though! Check this out http://www.zoneedit.com/doc/faq.html#faq42