DMARC

DMARC is used to tell receiving mail servers how you want them to handle any email they receive that doesn’t pass SPF or DKIM checks.

This is the most important part of your email security strategy.

An email can be sent from a server that has an SPF policy, but is not linked to your domain.
An email can be sent from a server that signs the email with a valid DKIM signature, but is not linked to your domain.
DMARC works in tandem with the from address in the email and requires that either the SPF or DKIM check must both pass and be aligned with the from address in the email.

Your policy can have three possible outcomes:

• none - The email is accepted regardless of SPF or DKIM alignment.
• quarantine - The email is quarantined (usually put into spam).
• reject - The email is rejected and will not be delivered to the inbox.