DKIM(DomainKeys Identified EMail) is a TXT record that attempts to prevent spoofing and spam by using a digitally signed authentication method to prove the validity of the sender. Typically, a mail service provider (Such as Google, Outlook, or HostArmada) has its custom DKIM record, and they provide it to the user utilizing their service. A public-private key pair achieves the authentication method by cross-referencing the public key in your DKIM record with the private key the organization uses. This process determines if you have the right to deliver emails using the service they provide. The key can be inserted as a string inside the TXT record, or it can be a set as a CNAME record that points to the provider's DNS, which holds the private key.
An example of a DKIM record would look like this:
v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA1TI0DbwwiwMEki4TxnxJZkInBBslPA1LgLHWa9ZP0NwVRsswxLt1VLkORJOSnrZ8TKA3goV9r+ZG24IgDu+lxDgA2dV+e+OC7QWNQqUxr+xo1+ytsSMonVg8Dlh/jEc1UGg/EKrIPCefz3gfOqGdBwqmyxYDy/4TAVj6zLDzWnuq/lgBYbrAmgb4f5YcjlOSqVVCibAKvsAtCOg852gJ+ryUNirZ+fk4/mTot1E4qtN4j9PBHjlRbKAzjq1snE6CDNbd7lTQeVzslBWpzhF4NX+6Oxi4OQ1HR6Kuh5bOh0Vsh99JDhq42vFmEgHqob3+bPaQ3Y/4Nv8r9KUi5qsFAQIDAQAB;