DKIM (DomainKeys Identified Mail) is an email authentication technique that allows the receiver to check that an email was indeed sent and authorized by the owner of that domain. It works together with DMARC (and SPF).
Read more about this topic in our article about DKIM signature
In order to implement DKIM you’ll need to have a valid DKIM record. You can use a DKIM Checker to check your DKIM record. A DKIM Checker or DKIM Analyzer tool will test the domain name and selector for a valid published DKIM record. DKIM authenticates the reputation and identity of the sender. We strongly recommend you to carefully test any updates to your DKIM records before applying them.