Check the PTR record for any IP. A properly configured PTR that matches the EHLO hostname is required for deliverability to most ISPs.
PTR Record Lookup: Why Reverse DNS Matters for Email Deliverability
A PTR (pointer) record maps an IP address to a hostname — the reverse of an A record. For email deliverability, the PTR record of your sending IP is checked by most major mail servers as a basic verification step. An IP without a valid PTR record, or with a PTR that doesn't forward-resolve back to the same IP, is a common cause of deferred or rejected mail that's easy to miss.
Forward-Confirmed Reverse DNS (FCrDNS)
FCrDNS means the PTR record's hostname also has an A record pointing back to the original IP. For example: IP 203.0.113.1 → PTR → mail.yourdomain.com → A record → 203.0.113.1. This loop confirms the PTR is legitimate. Gmail explicitly documents FCrDNS as a sending best practice, and several DNSBLs (including Spamrats NoPTR) specifically list IPs that fail this check.
Setting Your PTR Record
PTR records are managed by the IP owner — your server host or ISP, not your domain registrar. Contact your hosting provider and request a custom PTR (reverse DNS) record be set for your IP. The hostname should be meaningful: mail.yourdomain.com or smtp.yourdomain.com is ideal. All dedicated IP clients at Cloud Server for Email get custom PTR records as standard.
My PTR is generic (e.g. 203-0-113-1.static.isp.net). Is this a problem?
Yes. Generic PTR records are flagged by many spam filters as a signal of residential or shared hosting. While a generic PTR usually won't cause outright rejection, it can contribute to higher spam scores. Request a custom PTR from your IP provider pointing to a meaningful hostname under your domain.
Does PTR affect Spamhaus PBL listing?
Spamhaus PBL lists IPs that should not send direct-to-MX email — typically ISP dynamic and residential ranges. PBL listing is determined by the IP's network allocation, not its PTR record. However, a legitimate dedicated business IP with a proper PTR record is less likely to be in a dynamic/residential netblock. Check your IP against the IP Blacklist Checker to see if it's on PBL.