HELO/PTR hostname quality
Sending Infrastructure · High priority
What it is
The HELO/EHLO name should be a real FQDN matching the PTR, and the PTR should not look dynamic/residential (e.g. contain the raw IP or 'dynamic'/'dhcp'/'pool').
How to fix it
Use a static, branded FQDN for HELO that matches the PTR; avoid dynamic-looking reverse DNS.
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