Ever since 1.3, Minecraft has used SRV records to locate servers. However, Mojang seems to have failed to register "minecraft" as a service name, and is instead squatting on the name.

This is easily fixed: you can register the service name with IANA [here|https://www.iana.org/form/ports-services].

You should also consider registering TCP port 25565, which Minecraft is also squatting on. It uses the same form.