Email
How to Fix SPF PermError: Too Many DNS Lookups
Your SPF record broke silently and you didn't notice until mail started bouncing. Here is how to diagnose and fix the 10-lookup limit with flattening.
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OpsCheck Blog
Practical guides for system administrators, hosting engineers, and network professionals.
Email
Email Deliverability Checklist: DNS, Authentication, and Reputation
A practical checklist for troubleshooting email deliverability — DNS records, SPF/DKIM/DMARC authentication, blacklist monitoring, and SMTP reputation.
Security
DNSSEC Validation: How to Check If Your Domain Is Properly Signed
Learn how to verify DNSSEC chain of trust from root to your domain using command-line tools and catch misconfigurations before they cause resolution failures.
DNS
DNS Record Types Explained: A, AAAA, CNAME, MX, TXT, NS, SOA, PTR
Every DNS record type serves a specific purpose in connecting users to services. Learn what A, AAAA, CNAME, MX, TXT, NS, SOA, and PTR records do and how to verify them with command-line tools.
DNS
DNS Propagation: Why Your Changes Aren't Visible and How to Fix It
DNS changes take time to propagate through caches across the internet. Learn what TTL really controls, how to check propagation status, and what to do when your changes refuse to appear.
Email
Understanding DMARC Aggregate Reports (rua): XML Decoded
Your DMARC aggregate reports are piling up in a mailbox unread. Here is what the XML actually means and how to extract actionable data from it.
Security
How to Detect Phishing Domains Using DNS and SSL Tools
Spot fraudulent domains before they trick your users by analyzing DNS records, WHOIS registration data, SSL certificates, and blacklist status with freely available command-line tools.
SSL/TLS
7 Common SSL/TLS Errors and How to Fix Them
SSL certificate errors bring production sites down with cryptic browser warnings. This guide covers the seven most common SSL/TLS errors — name mismatches, expired certs, incomplete chains, mixed content, protocol mismatches, revoked certificates, and weak ciphers — with step-by-step fixes for each.
DNS
CNAME vs A Record: When to Use Each and Common Pitfalls
Understand the difference between CNAME and A records, when to use each, apex limitations, performance implications, and the real-world mistakes that break DNS for production domains.
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