If you want to be pedantic... not in the relevant case, no. In the relevant case (the domain is syntactically invalid but the naïve check didn't discover that)

If you want to be pedantic... not in the relevant case, no. In the relevant case (the domain is syntactically invalid but the naïve check didn't discover that) the response without MX RRs already tells you that there won't be an A (or AAAA).