A reverse DNS lookup that checks the round trip
Forward DNS turns a name into an IP; reverse DNS does the opposite, using a PTR record to map an IP address back to a hostname. This reverse DNS lookup takes an IP address — or a domain, which it resolves to its IPs first — and finds the PTR hostname each IP points to. But it doesn't stop at the PTR record, because a PTR on its own is only half the story.
PTR record checker with forward confirmation (FCrDNS)
The check that actually matters, especially for email, is forward-confirmed reverse DNS. A mail server receiving a connection doesn't just look up the PTR record; it then resolves that hostname forward and checks whether it points back to the same IP. If it does, the reverse DNS is "forward-confirmed" and trusted; if the PTR points to a hostname that resolves elsewhere, the setup looks misconfigured or spoofed and mail is far more likely to be rejected. This PTR record checker does that full round trip for you — IP to PTR hostname, hostname back to IP — and tells you plainly whether it confirms.
Why rDNS matters for sending mail
Receiving mail servers treat missing or non-confirming reverse DNS as a strong spam signal, because legitimate mail servers almost always have proper rDNS while botnets and compromised hosts often don't. So if your outbound mail is landing in spam or being rejected outright, a broken PTR record is one of the first things to check. That said — and this is worth being clear about — valid reverse DNS is one factor among several. Deliverability also depends on SPF, DKIM, DMARC, your IP's reputation, and blocklist status. A confirmed PTR is necessary but not sufficient on its own.
Reading the result
For each IP we show the PTR hostname it resolves to, then whether that hostname forward-resolves back to the same IP. A green confirmation means the round trip matches — the ideal state. An unconfirmed result means a PTR exists but points somewhere that doesn't resolve back, which is the misconfiguration to fix. And no PTR at all means the IP has no reverse record, which for a mail-sending IP is usually something to set up with whoever controls the IP block (often your hosting provider, since reverse DNS is delegated to the IP owner).