Learn what NS records are, how DNS delegation works, why NS records are the first thing to check when DNS fails, and how to use a free NS lookup tool to verify nameserver configuration.
Learn how reverse DNS works, what PTR records reveal about IP addresses, why forward-confirmed reverse DNS matters for email, and how to use a free reverse DNS lookup for security and diagnostics.
Learn how IPv4 subnetting works, what CIDR notation means, how to calculate network addresses, host ranges, and usable hosts, with real examples — plus an IPv6 intro and a free subnet calculator.
Learn how DMARC works, what the none/quarantine/reject policies mean, how to read a DMARC record, and how to use a free DMARC lookup to diagnose email authentication and spoofing protection.
Learn how SSL certificates work, what DV/OV/EV and wildcard certificates mean, how to read SSL checker results, and how to catch certificate expiry before users see browser security warnings.
Learn what BIMI is, how it works alongside DMARC and DKIM to display brand logos in email inboxes, what a BIMI lookup reveals, and how to implement it for your domain.
Learn how email spam blacklists work, why you might get listed, how to check if your IP or domain is on a blacklist, and how to get removed from the major DNSBLs.
Learn how traceroute works, how to read hop-by-hop latency results, what * * * means, how to identify congested hops, and how to use a free online traceroute tool for network diagnostics.
Learn what WHOIS reveals about domain ownership, registration dates, expiry, nameservers, and domain status codes — with real examples for security research, competitive analysis, and domain recovery.
