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ArostikVLARCK

Micro-Technology Solutions

DNS Resolution & Email Deliverability

Inspector of DNS & Mail Records

Look up any domain's DNS records and check whether SPF and DMARC protect its mail.

Recent lookups

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.

🥇

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.

📄

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.