ShowDNS Guides
Step-by-Step Guides for
DNS, SSL & Security
Practical walkthroughs with commands, checklists, and screenshots — everything you need to configure, fix, and validate your domain infrastructure.
Quick start — most popular
Jump to the most-read guides to solve common DNS and security problems.
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Featured guides
How to Fix an HSTS Error
Understand why HSTS errors appear and fix NET::ERR_CERT issues as a site owner or visitor.
FeaturedHow to Enable Perfect Forward Secrecy
Configure PFS on Apache and Nginx with ECDHE cipher suites and DH parameters for stronger TLS.
FeaturedHow to Check DNS Propagation
Check DNS propagation after a record change using online tools, dig, and nslookup step by step.
FeaturedHow to Flush DNS Cache
Flush DNS cache on Windows, macOS, Linux, and Chrome browser with step-by-step commands.
FeaturedHow to Create an SPF Record
Build and publish an SPF record for Google Workspace, Microsoft 365, and custom mail servers.
FeaturedHow to Configure DMARC
Set up DMARC from p=none monitoring to p=reject enforcement with a safe, staged rollout plan.
DNS
12How to Check DNS Propagation
Check DNS propagation after a record change using online tools, dig, and nslookup step by step.
How to Fix DNS Propagation Issues
Diagnose and fix slow DNS propagation — from high TTLs and stale caches to resolver delays.
DNS Propagation Time Explained
Understand how long DNS propagation takes, what factors affect it, and how to speed it up.
How to Flush DNS Cache
Flush DNS cache on Windows, macOS, Linux, and Chrome browser with step-by-step commands.
How to Troubleshoot DNS Problems
A complete DNS troubleshooting guide — from NXDOMAIN and SERVFAIL errors to NS misconfigurations.
How to Check Nameservers
Check nameservers for any domain using the ShowDNS NS Lookup, nslookup, dig, and whois.
Security
15How to Fix an HSTS Error
Understand why HSTS errors appear and fix NET::ERR_CERT issues as a site owner or visitor.
How to Enable Perfect Forward Secrecy
Configure PFS on Apache and Nginx with ECDHE cipher suites and DH parameters for stronger TLS.
How to Enable HSTS
Add Strict-Transport-Security on Nginx, Apache, and Cloudflare with a safe staged rollout.
How to Configure CSP
Deploy Content Security Policy in report-only mode, analyse violations, and move to enforcement.
How to Check Security Headers
Audit HTTP security headers using ShowDNS, curl, and browser DevTools — with fixes for missing ones.
Security Headers on Nginx
Add HSTS, CSP, X-Frame-Options, and other security headers to Nginx with config examples.
Email Security
5How to Create an SPF Record
Build and publish an SPF record for Google Workspace, Microsoft 365, and custom mail servers.
How to Configure DMARC
Set up DMARC from p=none monitoring to p=reject enforcement with a safe, staged rollout plan.
How to Setup BIMI
Configure BIMI to display your brand logo in Gmail, Apple Mail, and Yahoo Mail — including VMC.
How to Check MX Records
Verify MX records for email delivery using the ShowDNS MX Lookup tool, dig, and nslookup.
Why Emails Go to Spam
Diagnose and fix email deliverability issues — from missing SPF/DKIM/DMARC to blacklisted IPs.
SSL
3How to Install an SSL Certificate
Install an SSL certificate on Nginx and Apache using Let's Encrypt Certbot or a paid CA.
How to Fix SSL Errors
Fix SSL errors — expired certificates, hostname mismatches, incomplete chains, and mixed content.
How to Check SSL Configuration
Audit your SSL setup — certificate chain, TLS version, cipher suites, OCSP stapling, and HSTS.