dkim record audit

Audit DKIM selector records. The key length follows from the length of the encoded public key, so a short RSA key is readable from the record itself with no cryptography. Reports a key shorter than a stated minimum; a selector left in testing mode, which asks receivers to treat a failure as unsigned so it cannot contribute to DMARC alignment however correctly it signs; a revoked key, with its consequence; and a key type verifiers do not implement.