Domain Keys Identified Mail (DKIM) authentication allows the recipient to detect modification of the message body, including the from address, and attachments.   DKIM uses a digital signature stored in the email envelope that can be used by the recipient to authenticate the message.

DKIM is set-up in the mail server, so you will need to follow the instructions for your mail server.  Setting up DKIM typically involves:

  1. Generating cryptographics keys for your domain.
  2. Adding a record to you DNS based on the cryptographic keys you generated.
  3. Turning DKIM signing on.

It may sound complicated, however, most mail systems that support DKIM profile will guide you through this step by step. 

DKIM support articles for some common mail providers