Registro DNS A / AAAADNS
What is a DNS A and AAAA record?
An 'A' record maps human-readable domain hostnames to 32-bit IPv4 addresses; a 'AAAA' record resolves hostnames to modern 128-bit IPv6 endpoints.
DNS & NAME RESOLUTION
Inspector of DNS & Mail Records
Audit A, AAAA, MX, TXT, NS and CNAME records with SPF/DMARC security validation and email deliverability diagnostics.
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Your last looked-up domains will show up here, only in this browser.
Domain Name System (DNS) & Email Architecture
Root servers hierarchy, authoritative zones, record types, and SPF/DMARC security.
Global Hierarchy & Root Nameservers
The DNS namespace originates at 13 root server clusters (A-M), delegating queries to Top-Level Domains (.com, .org) and down to authoritative nameservers.
Key Record Types: A, AAAA, CNAME, MX
A/AAAA map domains to IPv4/IPv6 addresses. CNAME provides an alias to another domain (never on the apex root), and MX lists prioritized mail exchange hosts.
Anti-Spoofing Security: SPF, DKIM & DMARC
SPF declares authorized sending IPs. DKIM cryptographically signs outgoing emails, and DMARC dictates enforcement policy (p=reject / p=quarantine) on spoofed mail.
TTL (Time to Live) & Recursive Caching
TTL specifies the caching lifespan (in seconds) on recursive resolvers before querying authoritative nameservers, dictating record propagation speed.
DNS Propagation & Email Deliverability Troubleshooting
Step-by-step fixes for stuck TTL caches, mail delivery drops, and MX routing.
Issue 1
Slow DNS Propagation: Resolving to Old IP Hours Later
⚡ Quick Fix:Flush local resolver with `ipconfig /flushdns` and purge public DoH caches via dns.google/cache and 1.1.1.1/purge-cache.
🔧 Technical Fix:Lower the TTL to 300 seconds 24 hours prior to server migrations, then return it to 86400 once cutover succeeds.
Issue 2
Emails Bouncing or Landing in Spam Folders
⚡ Quick Fix:Use the SPF/DMARC generators on this tool to append your mail provider's official TXT records.
🔧 Technical Fix:Unify multiple SPF records into a single TXT with combined `include:` tags. Gmail & Yahoo reject mail lacking valid DMARC alignment.
Issue 3
ERR_TOO_MANY_REDIRECTS / CNAME Redirection Loops
⚡ Quick Fix:Switch Cloudflare SSL mode from 'Flexible' to 'Full (Strict)' to eliminate HTTP/HTTPS ping-pong.
🔧 Technical Fix:Ensure apex domain hosts an authoritative A record and www points via CNAME without cyclic server rewrites.
Issue 4
MX Host Missing A Record / Delivery Failures
⚡ Quick Fix:Check the table above: if flagged with 'Needs A record', add an A record for that mail host (e.g. mail.domain.com).
🔧 Technical Fix:RFC 5321 mandates MX targets must resolve to an FQDN with an authoritative A/AAAA record, never a raw IP or CNAME alias.
Did You Know? DNS Trivia & Facts
Historical trivia about the 13 root clusters, hosts.txt origin, and symbolics.com.
🌍
The 13 Root Server Letters That Power the World
There are only 13 root IP addresses (A through M) due to the historic 512-byte UDP packet limit. Through Anycast, they are mirrored across 1,700+ physical datacenters.
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symbolics.com: The First Domain Registered in 1985
Registered on March 15, 1985 by Symbolics Inc., `symbolics.com` is the oldest registered .com domain and remains online today as an Internet museum.
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When the Entire Internet Was a Single Text File (hosts.txt)
Before Paul Mockapetris created DNS in 1983, Elizabeth Feinler at SRI manually updated a master `hosts.txt` file and distributed it weekly via FTP.
🛡️
The 2008 Kaminsky Bug & The Dawn of DNSSEC
Dan Kaminsky discovered a flaw enabling DNS cache poisoning in under 10 seconds. The secret patch assembly in 2008 accelerated global adoption of cryptographic DNSSEC.
DNS Records & Email Authentication Glossary
Learn the fundamental concepts, protocols, and technical terminology of this tool.
Registro MX (Mail Exchange)Correo
What is a DNS MX record?
Designates the destination mail transfer agents (MTAs) authorized to accept inbound email messages for a domain, prioritized by integer weightings.
Registro SPF (Sender Policy Framework)Seguridad
What is a DNS SPF record?
A public TXT record publishing authorized outbound SMTP IP blocks permitted to originate email on behalf of a domain, curbing spoofing.
Política DMARCCorreo
What is a DMARC policy?
An authentication policy aligning SPF and DKIM outcomes to command receiving inboxes whether to quarantine or outright reject fraudulent emails.