Guides
How DNS, nameservers, DNSSEC, SSL certificates and email authentication actually work, and how to troubleshoot them. Each guide links to the tool that checks what it describes.
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DNS Record Types Explained: A, CNAME, MX, TXT & More
The ten record types you will meet most often, what each one is for, and how they go wrong.
9 min read
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How DNS Delegation Works: NS, Glue & Subdomains
Follow a lookup from the root to your zone, see where registrar settings fit in, and delegate a subdomain.
9 min read
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DS vs DNSKEY vs RRSIG: DNSSEC Records Explained
The three record types behind DNSSEC and how a resolver uses them to validate an answer.
8 min read
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DNSSEC Validation Failed? Fix DS Mismatch & SERVFAIL
Stale DS records, provider migrations, expired signatures and the other ways DNSSEC breaks.
9 min read
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DNS SERVFAIL Error: What It Means and How to Fix It
What SERVFAIL means, its four common causes, and a step-by-step way to find which one you have.
6 min read
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Recursive vs Authoritative DNS: What's the Difference?
Why the resolver your laptop asks and the server holding your records can disagree.
7 min read
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How Long Does DNS Propagation Take? Why It Varies
TTLs, negative caching and the real reasons "propagation" seems random—with timings per change.
8 min read
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DNS_PROBE_FINISHED_NXDOMAIN: Causes and Fixes
Tell a local DNS problem from a missing domain, then fix it as a visitor or a site owner.
6 min read
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How SSL Certificates Work: Chain of Trust Explained
What a certificate proves, how the chain of trust works, and what a browser checks before showing the padlock.
8 min read
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How to Check SSL Certificate Expiry and Avoid Outages
Check the expiry date, understand shrinking lifetimes, and find out why automated renewal still fails.
8 min read
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Fix SSL Certificate Errors: NET::ERR_CERT Codes
Name mismatches, missing intermediates, self-signed certificates and handshake failures, by error code.
9 min read
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HTTP to HTTPS Redirects, HSTS & Too Many Redirects
Getting every visitor onto HTTPS, fixing redirect loops, and keeping visitors on HTTPS with HSTS.
8 min read
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SPF, DKIM and DMARC Explained (Gmail & Yahoo Rules)
The three records that prove your mail is really from you, and how receivers combine them.
9 min read
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How to Find Your DKIM Selector and Check the Record
Find the selector in a real message header, look up the key, and spot the problems that break it.
6 min read
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SPF PermError: Too Many DNS Lookups (How to Fix)
How includes add up to a permerror, and how to trim them safely.
6 min read
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Why Are My Emails Going to Spam? How to Find and Fix It
The two checks that explain most spam-folder mail: blacklists and authentication, and how to fix each.
7 min read
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New Domain Checklist: What to Do After You Buy a Domain
The day-one steps that protect a new registration, and the setup to finish before you rely on it.
8 min read
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DMARC p=none to p=reject: A Safe Rollout Plan
A safe, report-driven path from monitoring to full enforcement.
7 min read
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How to Set Up BIMI: Free vs VMC & CMC Logos
Get your logo into the inbox for free, or with a VMC or CMC, and know which inboxes each one reaches.
8 min read
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Nameserver Mismatch: Registrar vs Zone NS Records
Registrar vs. zone NS records, lame servers and how to clean up after a provider move.
7 min read