--- * RFC7505 also states that a NULLMX record must have a priority
--- of 0. We do not enforce this either. We ignore any records
--- containing an empty label (i.e. a single dot). Such a record will
--- not be deliverable anyway, and in light of the first item, means
--- that we will not \"incorrectly\" reject batshit-crazy domains
--- that have a NULLMX record (but with a non-zero priority) in
--- addition to other, valid MX records.
---
-
-validate_mx :: Resolver -> Domain -> IO Bool