Check MX record hostname validity (#358) #676

Job	Run time
lint	1m 1s
docker-build	37s
test	6m 34s
build (linux, amd64)	34s
build (linux, 386)	42s
build (linux, arm)	32s
build (linux, arm64)	38s
build (darwin, amd64)	37s
build (darwin, arm64)	32s
build (windows, amd64)	41s
build (windows, 386)	38s
build (windows, arm)	37s
build (windows, arm64)	31s
integration-test-serverside (f0023141ec429d912e329665f937d05b178a3fee)	2m 4s
integration-test-clientside (v0.13.2)	2m 8s
analyze	2m 21s
	20m 47s

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