Guides
Short how-to guides on certificates, email security and DNS.
Certificate expiry checklist for IT teams (2026–2029 changes)
Public TLS certificate lifetimes shrink from 398 to 47 days by 2029. A practical checklist to stop expired certificates taking client sites offline.
5 min readDangling DNS and subdomain takeover: how to find and fix it
How forgotten CNAME records let attackers take over a client's subdomain, how to find them, and the clean-up steps to add to every decommissioning checklist.
5 min readDKIM selectors explained: find, check and fix DKIM records
What a DKIM selector is, why you cannot list a domain's DKIM keys, how Microsoft 365 uses selector1 and selector2, and how to check key length and alignment.
5 min readDMARC policies explained: none, quarantine and reject
What DMARC p=none, p=quarantine and p=reject do, how alignment works with SPF and DKIM, and a safe path for moving a client domain to an enforcing policy.
6 min readRDAP vs WHOIS: how to check domain expiry in 2026
WHOIS is no longer required for most gTLDs. How RDAP works, how to read a domain's expiry date and registrar from it, and what to do when a registry has none.
5 min readSPF's 10 DNS lookup limit: why SPF fails and how to fix it
Why a valid-looking SPF record fails with permerror, which mechanisms count toward the 10-lookup limit, and safe ways to bring it back under.
5 min read