Guides
Plain-English explanations of the concepts behind our free diagnostic tools — DNS, email authentication, SSL/TLS, and uptime monitoring.
Email deliverability
What Is DMARC?
How DMARC builds on SPF and DKIM to stop email spoofing, and how to read a DMARC record.
Read more →SPF vs DKIM vs DMARC Explained
Three different email-authentication standards, three different jobs — how they fit together.
Read more →How to Fix Email Deliverability Problems
A practical diagnostic order for tracking down why mail is landing in spam or not arriving at all.
Read more →Email Blacklists Explained
How IP and domain blacklists work, why you can end up on one without sending a single spam message, and how delisting actually works.
Read more →SSL / security
SSL vs TLS: What's the Difference?
Why everyone still says "SSL" even though the protocol has been TLS for over two decades.
Read more →How to Monitor SSL Certificate Expiration
Certificate expiry is one of the most avoidable outages there is — here's how to actually stay ahead of it.
Read more →HSTS Explained
How HTTP Strict Transport Security stops a downgrade attack the certificate alone can't prevent.
Read more →DNS
What Is DNSSEC?
How DNSSEC cryptographically signs DNS records to stop cache poisoning and spoofed responses.
Read more →DNS Propagation Explained
Why a DNS change doesn't take effect everywhere at once, and what TTL actually controls.
Read more →How MX Records Work
Priority values, multiple mail servers, and what actually happens when the top-priority one is down.
Read more →Uptime / monitoring
What Is Synthetic Monitoring?
Simulating real user journeys instead of just pinging a URL — what it catches that uptime checks miss.
Read more →Uptime Monitoring vs Ping Monitoring
A host that answers ping isn't the same as a website that's actually serving pages — why the distinction matters.
Read more →How to Measure Website Availability
"Uptime percentage" hides more than it reveals unless you're precise about what counts as down.
Read more →SLA Monitoring Explained
How to actually prove you hit an uptime commitment, instead of just believing you did.
Read more →Status Page Best Practices
A status page that only gets updated after customers already noticed defeats its own purpose.
Read more →APIs
HTTP Status Codes Explained
What 2xx, 3xx, 4xx, and 5xx actually mean, and which ones should page someone at 3am.
Read more →REST API Monitoring Guide
What's actually worth checking beyond "did it return 200" — schema, latency, and auth expiry.
Read more →How to Test API Endpoints
A practical checklist for manually verifying an endpoint before you automate checking it.
Read more →