DKIM-Signature domain mismatch validation

[breedbekkikker]

The following DKIM-Signature validation is missing (probably in ValidateDkimSignatureParameters):

Verifiers MUST confirm that the domain specified in the "d=" tag is the same as or a parent domain of the domain part of the "i=" tag. If not, the DKIM-Signature header field MUST be ignored, and the Verifier should return PERMFAIL (domain mismatch).

Concerning the optional i= tag: If the DKIM-Signature header field does not contain the "i=" tag, the Verifier MUST behave as though the value of that tag were "@d", where "d" is the value from the "d=" tag.

See https://tools.ietf.org/html/rfc6376#section-6.1.1