What’s “policy rejections due to missing MX” really mean?

"Missing MX" policy rejection enforces sender domain standards:

What it means:

Receiving server checked your FROM domain. Found no MX records. Rejected based on policy.

Why receivers check:

Legitimate domains can receive mail. No MX suggests throwaway or fake domain. Anti-spam measure.

Domain MX requirements:

Domain should have MX records for receiving mail. Even if you only send, you should be able to receive. Bounces go to your Return-Path domain.

Common scenarios:

New domain not fully configured. Dedicated sending domain without MX. Misconfigured DNS.

Resolution:

Add MX record for sending domain. Point to a server that can receive (even if just bounces). Ensure Return-Path domain has MX.

No MX says "I can't receive mail." Receivers may distrust senders who cannot receive replies.