--
-- Examples:
--
--- The example domain, example.com, has no MX record.
+-- The example domain, example.com, has a NULLMX record.
--
-- >>> rs <- makeResolvSeed defaultResolvConf
-- >>> let domain = BS.pack "example.com."
-- >>> withResolver rs $ \resolver -> lookupMX' resolver domain
--- ("example.com.",Right [])
+-- ("example.com.",Right ["."])
--
lookupMX' :: Resolver -> Domain -> IO LookupResult
lookupMX' resolver domain =