Article is missing a note on the existence of MX records for the domains. Sure, you can easily have a send-only domain without an MX record, but the common case is likely to setup both send and receive capability. It would be interesting to have that number included as domains without MX and DMARC might just not be configured for email at all. Worst case the 45% of domains without DMARC are simply not relevant for email and thus not configured at all. I would find "x% of domains with configured email don't enforce DMARC" more interesting.