Reverse DNS (PTR) & FCrDNS Checker
Mail servers reject emails without valid Forward-Confirmed Reverse DNS (FCrDNS). Check if your mail server IP resolves to a hostname that resolves right back to your IP.
What is Forward-Confirmed Reverse DNS (FCrDNS)?
FCrDNS is a two-way authentication check. When you send an email from IP 198.51.100.10, the receiving mail server queries the PTR record in the in-addr.arpa zone to find your hostname (e.g., mail.example.com). Then, it resolves the A record of that hostname. If the forward IP matches your sending IP, FCrDNS passes.
Why Does Gmail & Yahoo Require FCrDNS?
Spammers frequently hijack residential DSL, cable, or dynamic cloud IPs with generic hostnames likecpe-12-34.isp.net. Since only the legitimate owner of an IP block or VPS can set a custom PTR record at their hosting provider (AWS, DigitalOcean, Hetzner, OVH), FCrDNS proves that you own and administer the mail server.
Looking for automated email deliverability?
CentricSell Mail automates IP allocation, PTR configuration, warmups, and failover across multiple ESPs.