PTR records and reverse DNS for email: setup and checks

Every receiver runs the same opening check on every connection: who is this IP, really? A reverse DNS (PTR) lookup is the cheapest way to ask. If your IP doesn't answer, or answers with generic nonsense, you've failed a vibes check before you sent a single byte of message.

For the broader infrastructure picture, use the reputation hub and keep PTR evidence alongside blocklists, provider dashboards, and domain-monitoring checks.

What a PTR record looks like

PTR records live in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zone. The IP is reversed and concatenated with the zone suffix. For 203.0.113.42 the PTR query is 42.113.0.203.in-addr.arpa.

Forward-confirmed reverse DNS (FCrDNS)

Receivers don't just check that a PTR exists — they check that the hostname it returns also resolves back to the original IP via an A or AAAA lookup. This is FCrDNS, and it's the actual gate. A mismatch is treated the same as no PTR at all.

# Step 1: PTR lookup
dig +short -x 203.0.113.42
# Returns: mail.example.com.

# Step 2: Forward lookup of the result
dig +short A mail.example.com
# Should return: 203.0.113.42

# If both match, FCrDNS passes.

Who sets the PTR

PTR for IPv6

Most major receivers — Gmail in particular — actively require PTR for IPv6 senders, often more strictly than for IPv4. The format is verbose: each hex digit reversed and dot-separated, ending in ip6.arpa. Most providers expose a friendly UI; you rarely write the raw record.

HELO/EHLO matching

The hostname your MTA announces in HELO/EHLO should match the PTR. Most filtering engines treat a HELO-PTR mismatch as another negative signal. Configure your MTA's myhostname (Postfix), dkimprovidername (Exim), or equivalent to match exactly.

# PTR for 203.0.113.42 returns mail.example.com
myhostname = mail.example.com
smtp_helo_name = mail.example.com

Verifying

1. Run dig +short -x <your-ip>. Expect a hostname on a domain you control.
2. Run dig +short A <returned-hostname>. Expect your IP back.
3. Send a test through WillItInbox — the report's infrastructure category breaks PTR results out individually.
4. Watch the message header — most receivers add an X-Originating-IP or Received: ... helo=... line that reveals what they thought of you.

The minimum healthy chain is one PTR hostname, a forward A or AAAA record returning the same IP, and an EHLO name consistent with that hostname. Use domain monitoring for recurring checks, the MX lookup for the receiving side of the route, and a deliverability test to see how the sender identity appears in the final report.