DomainKeys Identified Mail (DKIM) records allow a recipient to validate a sender as the owner of an email message.
Domain Keys use public-key encryption to apply digital signatures to email, this allows verification of the sender as well as of the integrity of the message in question.
Every time you send an email, it will contain an encrypted key that the receiving mail server will decrypt using a Public Key located in the DKIM record. This connection allows the receiving mail server to verify that the email is actually being sent by that domain.
You will need to obtain your Public Key from your mail service provider.
DKIM is created using TXT records. TXT records are plain text records with a name and a value of up to 255 characters.
Constellix supports TXT records longer than 255 characters.
Visit the Domain Key public website to learn more: DKIM.ORG