update DK to DKIM

If you have a "DKIM" record which does not begin with "v=DKIM1", then it may not be the current iteration of DKIM since the form is DK, which was deprecated over 15 years ago.  There is some backward compatibility in the DKIM specification so that this older format of key will work, but for the most part nobody should continue using it.

RFC 6376 indicates that use of the tag v=DKIM1 is highly recommended. Check your keys by either manual use of the DKIM Inspector, or by clicking on the selector links in the Detail Viewer.

Updating your key may require regeneration of the key-pair, but it *could* be as simple as just adding the tag in the public key.  Consult the person or organization in charge of signing with the specific selector+domain you are working with.