Is it mandatory to prescribe a DMARK policy?

Question

Email

Is it mandatory to prescribe the DMARK policy, does it affect the deliverability of emails?

Answer 1

DMARC. To implement or not to implement?

Answer 2

DMARC technology helps you authenticate the sender, track spam and phishing emails, and determine what to do with emails that fail verification. In fact, this is an add-on for DKIM and SPF, in which you can also specify how to deal with such letters. If you are engaged in mass mailings, it is better to register DMARK. For most email domains, the best DMARC setting would be:
_dmarc IN TXT "v=DMARC1; p=reject;", which would mean rejecting all messages that didn't pass validation.