Reverse DNS (PTR) + FCrDNS
Sending Infrastructure · Critical priority · hard-fail gate
What it is
The sending IP must have a PTR record that forward-resolves back to the same IP. Missing rDNS is a hard requirement failure at Gmail/Yahoo/Outlook.
How to fix it
Set a PTR record for your sending IP that points to a hostname whose A record points back to that IP.
This is a hard-fail gate. If it fails, Gmail / Yahoo / Outlook may junk or reject your mail regardless of everything else — so fix it first.
Check your email
See how your real email scores on this and every other deliverability factor.