DKIM

DKIM (DomainKeys Identified Mail) is an email authentication method. It helps the server receiving your email verify that it was sent from your domain.

In other words, DKIM helps to prevent email spoofing.

How DKIM works (see this section for a practical example):

• Two keys are generated on your server: a public key and a private key:
  • public key - you add it on the DNS server as a TXT record.
  • private key - it’s a secret key and should not be exposed to anyone.
• Your mail server adds a cryptographic signature to the SMTP header of email messages. The signature is generated using the private key.
• On the receiving side, the public key from your DNS server is used to verify the digital signature in the email SMTP header, ensuring that the email was not altered and was sent from your domain.

Check out this article to see how to add email functionality to the WordPress Docker image using a Postfix container with DKIM. Just follow the simple steps in sections 1, 2, and 3.

The same process, as described in the article, was used here on wpdiaries.com to add email-sending functionality with DKIM.

Please also see this section for a little bit more details on DKIM.