550 dkim encountered the following problem validating
In addition to the requirement mentioned that the i= domain must be the same as or a sub-domain of the d= domain, the d= and s= bits are used by the validator to look up the signer’s public DKIM key in DNS.
First, we’ll look at the ones that are mostly of passing interested to the reader: The reason these parts are of interest to the receiving server is that they provide the information necessary to help the receiver validate the signatures.
It’s been my experience that such failures drive more support tickets than any other kind of DKIM issue.
DKIM is an authentication method, which uses encryption with public/ private keys, to validate whether the emails are generated from the authorised servers, recognized and configured by the administrators of the sending domains.
When we speak of “Email Authentication”, we’re referring to a technique that provides to the recipient of a message some level of certainty that the message actually originated with the claimed source of the message.
The idea behind such techniques is to achieve some level of defense against fraudulent email, such as phishing and spoofing, mail that could erode a recipient’s trust in receiving email.