I have an Apex domain with two MX Records e.g. Example.com MX 10 cluster.host.com MX 20 cluster.host.com
This domain has a subdomain with a different MX record e.g. Sub.example.com MX 10 filter.host.com MX 20 filter.host.com
However when I do an NSLookup for the subdomain MX Record, I only get the Apex domain records.
I feel like I have missed something obvious... Does the subdomain "Sub" require an A Record in order for the MX to be detected?