DMARC records - test and update for a stricter policy

DMARC = Domain-based Message Authentication, Reporting, and Conformance

p="none" means  Policy = none.  Most are requiring p=reject or p=quarantine

rua=mailto:<an email address>    means send an aggregate report via email

MXToolbox.com = a website to test your own DMARC settings for your custom domain.

DNSChecker.org = another website to test your own DMARC records