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Networking explainers, guides, tutorials, and news.

DNS How Long Does DNS Propagation Take? Up to the old TTL for a record change, up to two days for a name server change. What sets the wait, how to shorten it, and how to check it with dig. Published October 2026 · 8 min read Email SPF, DKIM, and DMARC Explained: Why Email Goes to Spam What SPF, DKIM, and DMARC do, how alignment ties them together, and the mistakes that send mail to spam. Published September 2026 · 7 min read Security What Is SNI? How Server Name Indication Works and How to Test It How a client names the site it wants in the TLS handshake, what a server does with the name, and how to test it with a browser tool, openssl, and curl. Published August 2026 · 7 min read Email Is My IP Blacklisted? How to Check and Get Delisted How a DNSBL lookup works, what Spamhaus, Barracuda, SpamCop, and PSBL listings mean, and how to get removed from each. Published July 2026 · 7 min read Network diagnostics Why Ping Fails: 5 Causes Besides an Outage Five common causes of a ping timeout, and how to confirm whether a host is down. Published June 2026 · 4 min read Network diagnostics Understanding Traceroute: How to Read Every Hop How traceroute works, how to read every hop, and what timeouts and latency jumps mean. Published May 2026 · 5 min read Security SSL Certificate Expired? How to Fix It What causes it, how to renew it, and how to prevent it from happening again. Published April 2026 · 4 min read

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Host Check UpdatedStatus, redirects, DNS, and more PingIs it up, and how fast? DNS LookupRecords and how they resolve TracerouteThe path, hop by hop WHOISOwner, registered, expires SSL CheckIs the certificate valid? Security Headers NewBrowser security headers Blacklists NewSpam and abuse lists DNS Propagation NewHas your DNS change spread? Email Check NewSPF, DMARC, and DKIM