Description
FortiDirector can be used to Load Balance your MX Records. While FortiDirector does not specifically handle MX records, it can be used to respond to the DNS lookup for an MX record, and that DNS response can include all the traffic shaping features and monitoring results of the FortiDirector solution.
The major restriction to load balancing MX records is that the DNS lookup response can only be a DNS A Record, according to RFC 2181 section 10.3:
The domain name used as the value of a NS resource record, or part of the value of a MX resource record must not be an alias [CNAME].
The drawback being that when adding your Network Resources for this particular type of scenario, you must add in the "Target Host" as an IP Address, not a hostname. Hostnames have been known to work in older or less-strict mail clients, but newer and stricter clients which adhere to the RFC will not.
Therefore, to build your MX Load Balanced solution, you would configure your Network Resources using IP Addresses. This will cause the DNS Redirects to respond with an A record, rather than a CNAME record (which occurs when the Target Host is set to a hostname), and meet the requirements of the RFC.
An example of Network Resources that will result in an A Record DNS response is in the image below:
