Check MX record hostname validity #662

Job	Run time
test	6m 34s
lint	2m 17s
docker-build	37s
build (linux, amd64)	33s
build (linux, 386)	36s
build (linux, arm)	30s
build (linux, arm64)	31s
build (darwin, amd64)	34s
build (darwin, arm64)	37s
build (windows, amd64)	41s
build (windows, 386)	31s
build (windows, arm)	38s
build (windows, arm64)	31s
analyze	2m 10s
integration-test-clientside (v0.13.2)	2m 15s
integration-test-serverside (f0023141ec429d912e329665f937d05b178a3fee)	2m 16s
	21m 51s

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