How does DMARC work, briefly, and in non-technical terms?
A DMARC policy allows a sender to indicate that their messages are protected by SPF and/or DKIM, and tells a receiver what to do if neither of those authentication methods passes – such as junk or reject the message. DMARC removes guesswork from the receiver’s handling of these failed messages, limiting or eliminating the user’s exposure to potentially fraudulent & harmful messages. DMARC also provides a way for the email receiver to report back to the sender about messages that pass and/or fail DMARC evaluation.
Want a more technical overview - visit dmark.org here https://dmarc.org/overview/
Here is an extensive list of resources: https://dmarc.org/wiki/FAQ