DNS Tools — DNS Record Lookup, MX, NS, SPF & Reverse DNS

The Domain Name System (DNS) is the distributed database that maps human-readable domain names to IP addresses and routes email. Every internet connection begins with a DNS query. DNS tools make it possible to inspect, verify, and troubleshoot the records behind that process without installing command-line software.

Webmasters use DNS Lookup to confirm A and AAAA records are correctly pointed to their hosting server after a migration. Mail server operators run MX Lookup and SPF Lookup to diagnose email deliverability failures — a missing or incorrectly formatted SPF record (RFC 7208) is the most common reason outbound email is rejected or filtered to spam. Network engineers use Reverse DNS Lookup to verify that a server's PTR record matches its hostname, a requirement for inbox delivery at Gmail and Microsoft.

Each DNS tool on this page targets one or more record types. The table below defines each type, its protocol standard, and its primary use case.

When email from a domain is failing delivery or landing in spam, the following sequence of DNS lookups identifies the root cause. Each step links to the relevant tool.

1. MX Lookup — Verify the domain has a valid MX record and the mail server hostname is correct and reachable.
2. SPF Lookup — Confirm the SPF TXT record (RFC 7208) authorizes the sending mail server's IP address.
3. TXT Lookup — Check all TXT records including DKIM public key records and the DMARC policy record.
4. Reverse DNS Lookup — Verify the mail server's IP resolves to its expected hostname (PTR record). Gmail and Microsoft require a FCrDNS match for inbox delivery.
5. IP Blacklist Checker — Confirm the mail server's IP is not listed on any DNSBL used by inbox providers to filter spam.

Diagnosing email deliverability failures: A mail server admin notices outbound email landing in spam at Gmail. Running MX Lookup confirms the correct mail server hostname is listed. SPF Lookup reveals the TXT record was last updated before a new sending IP was added — the omitted IP is the reason Gmail is rejecting messages. Updating the SPF record and rerunning SPF Lookup confirms the fix within seconds.

Verifying a DNS change has propagated: A developer points a domain's A record to a new server IP but still sees the old IP when testing. Running DNS Lookup against the domain's authoritative name server confirms the change is live. Running the same query against Cloudflare (1.1.1.1) returns the old cached value — still valid for the remaining TTL on the old record. No propagation failure exists; the cache clears automatically when the TTL expires.

Setting up FCrDNS for a new mail server: A sysadmin provisions a new mail server and needs forward-confirmed reverse DNS before Gmail will accept mail from the new IP. Reverse DNS Lookup verifies the IP resolves to the expected hostname. Website to IP Lookup confirms that hostname resolves back to the same IP. Both must match for FCrDNS compliance — a requirement documented in the Gmail Postmaster Guidelines and Microsoft's email sender requirements.