The DKIM Record tool will test a domain name and selector for a valid published DKIM key record. DomainKeys Identified Mail (DKIM) defines a domain-level digital signature authentication framework for email by permitting a signing domain to assert responsibility for a message in transit. DKIM authenticates the reputation and identity of the sender and their email signing practices for additional handling such as delivery.
DKIM operates by authenticating the identity of the message signer from the purported author of the message allowing for verification of responsible senders and the integrity of the message contents. This authentication of responsibility for a message is validated via a cryptographic signature and querying the signer’s domain to retrieve a public key.
What this means: A DKIM record is a component of a system that allows your server to cryptographically sign your email messages so that recipients can, if they like, confirm that a message came from you.
A DKIM Selector is text that is added with the domain to create a unique DNS record used during DKIM. This allows multiple keys to exist under one domain which allows for different signatures to be created by different systems, date ranges, or third party services.