DMARC is a message authentication method that combines SPF and DKIM to ensure that messages are not forged. It is predominantly used (and recommended for use) by companies who send mail likely to be phished, like financial services companies.
Because messages that fail DMARC cannot be forwarded to any provider that checks DMARC, we recommend its use by all accounts. It is presently included in the standard spam filtering group, but it may be added to all accounts soon.
In general, mail picked up by the DMARC filter is likely to be phishes and other forged spam. However, it may also pick up mail for domains which may have made their rules overly restrictive, or mailing list mail sent via software that does not handle DMARCed domains properly.
Due to the wide range of methods and places that Pobox users can send mail from, it is not typically appropriate for use with your personal mail, and we do not publish DMARC rules for our domains at this time.