p=none is the DMARC notation for the None policy. It instructs the receiver to authenticate incoming email via DMARC but to take no action based on authentication results. The receiver will include the results of this policy action in the DMARC reports for that domain.
Often referred to as monitoring mode, the p=none policy setting is useful for evaluating the impact of DMARC, and to validate that SPF and/or DKIM are correctly configured for legitimate senders. Because all authentication results are reported to the domain owner, p=none can shed light on whether or not services are correctly authenticating.
The advantage of monitoring mode is that administrators can assess their state of email authentication with no risk of compromising delivery of important mail messages. However, this mode does nothing against unauthorized messages such as phishing emails. Blocking unauthorized email is the primary purpose of the DMARC specification, meaning that long term use of p=none is unlikely to be in the domain owner’s best interest.
We recommend using p=none as a first step in implementing DMARC. Once you have discovered and resolved any issues with your legitimate senders, you should move to a quarantine (p=quarantine) or reject (p=reject) policy.