DKIM Core is a way to attach a token (or tokens) to an email that tells the recipient who is responsible for the email (typically the token would represent the author of the email, the operator of the email service, or the owner of a mailing list, but it might also represent others, such as email reputation or certification services). The DKIM Core specification is a simplified subset of DKIM.

Any email that attaches a DKIM Core token is also validly DKIM signed. This means that receivers and spam filters don’t need to do anything differently to support DKIM Core - if they support DKIM, they already support DKIM Core.

according Bryan Quilty, this is the LOUDEST email he's ever received