What are the different DMARC policies (none, quarantine, reject) and which should I start with?

DMARC policies dictate how receivers should handle emails failing authentication. 'none' monitors email flow without taking action, providing valuable data. 'quarantine' instructs receivers to place failing emails in spam folders. 'reject' instructs receivers to reject failing emails. It's recommended to start with 'none' to monitor your email ecosystem, then move to 'quarantine' after verifying legitimate email sources, and finally to 'reject' once you're confident in your DMARC configuration.