DKIM (Domain Keys Identified Mail) is an email authentication technique that allows someone to check and confirm whether an email they have received was actually sent and authorized by the owner of a domain. This is done by giving the email a digital signature called the DKIM signature which is added to a message and encrypted. DKIM helps by detecting forgery and protecting from email spam and possible phishing attacks.
A DKIM selector is part of the DKIM record and it's purpose is to allow the publishing of multiple DKIM keys on any domain. To find a DKIM selector please follow the steps given below: