Reverse (PTR) lookup
52.101.40.5
52.101.40.5 is mail-cy4pr03cu00105.inbound.protection.outlook.com.
What name does this IP address claim, and does it point back? The name and the address agree, which is what mail servers want to see.
- 3 OK
- Reverse name queried
- 5.40.101.52.in-addr.arpa
Reverse DNS for 52.101.40.5
| Name (PTR) | TTL | That name's address | Points back |
|---|---|---|---|
| mail-cy4pr03cu00105.inbound.protection.outlook.com | 10 | 52.101.40.5 | Yes |
Tests
-
OK
Reverse DNS record published
52.101.40.5 reverses to mail-cy4pr03cu00105.inbound.protection.outlook.com.
More info about “Reverse DNS record published”
Reverse DNS turns an IP address back into a name. Mail servers check it on every incoming connection: an address with no reverse name, or one whose name does not point back to it, looks like a home connection or a compromised machine, and its mail is more likely to be refused. The reverse name is set by whoever provides the IP address (your hosting company or ISP), not in your own DNS zone.
-
OK
Reverse name points back (forward-confirmed)
mail-cy4pr03cu00105.inbound.protection.outlook.com points back to 52.101.40.5 — forward-confirmed reverse DNS.
More info about “Reverse name points back (forward-confirmed)”
Reverse DNS turns an IP address back into a name. Mail servers check it on every incoming connection: an address with no reverse name, or one whose name does not point back to it, looks like a home connection or a compromised machine, and its mail is more likely to be refused. The reverse name is set by whoever provides the IP address (your hosting company or ISP), not in your own DNS zone.
-
OK
Reverse name is specific
The reverse name looks like a named server, not a generic ISP address.
More info about “Reverse name is specific”
Many spam filters penalise mail from addresses whose reverse name looks auto-generated (it contains the IP address, or words like dynamic or dhcp), because that pattern usually means a home or office connection.
How we got this answer
Every question we asked, in order, with how long each server took to reply.
-
recursive resolver — asked 5.40.101.52.in-addr.arpa SOA
· 60 ms
The zone holding 5.40.101.52.in-addr.arpa is 40.101.52.in-addr.arpa. -
ns1-09.azure-dns.com (13.107.236.9) — asked 5.40.101.52.in-addr.arpa PTR
· 24 ms
1 PTR record returned (authoritative).
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