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- Browser errors · TroubleshootingERR_EMPTY_RESPONSE: when the server sends no dataThe server closed the connection without a reply. Crashed workers, rules that drop requests on purpose, and proxies that give up silently.October 5, 2026 · 3 min read
- SSL · Browser errorsNET::ERR_CERT_DATE_INVALID: expired certificate or wrong clock?How to tell whether the certificate expired or the device clock is wrong, how to renew and reload properly, and how to never be surprised by it again.October 5, 2026 · 3 min read
- SSL · Browser errorsNET::ERR_CERT_COMMON_NAME_INVALID: certificate doesn't match the domainThe certificate is for a different name. www vs bare domain, wildcard limits, default certificates and DNS pointing elsewhere.October 5, 2026 · 3 min read
- SSL · Browser errorsNET::ERR_CERT_AUTHORITY_INVALID: untrusted certificate fixesSelf-signed certificates, private CAs, and the sneaky one: a missing intermediate that works in your browser and fails everywhere else.October 5, 2026 · 4 min read
- SSL · Browser errorsERR_SSL_PROTOCOL_ERROR and ERR_SSL_VERSION_OR_CIPHER_MISMATCH explainedWhen HTTPS can't be set up at all: plain HTTP on port 443, outdated TLS versions and missing edge certificates, and how to test the handshake.October 5, 2026 · 4 min read
- Email errors · Email550 5.7.26: fix Gmail's 'unauthenticated email' bounceGmail rejects mail that fails SPF, DKIM or DMARC. How to find which check failed, the usual causes, and what Gmail, Yahoo and Outlook now require.October 5, 2026 · 4 min read
- Email errors · Email550 5.1.1 user unknown: why email bounces and what to doThe mailbox doesn't exist. How to read email error codes, what to check as the sender, and what to fix when real addresses on your domain bounce.October 5, 2026 · 3 min read
- Email errors · Email554 5.7.1 message rejected: blocklists, reverse DNS and relay errorsA policy rejection with four usual reasons: a blocklisted IP, missing reverse DNS, failed authentication or relay denied. How to tell which and fix it.October 5, 2026 · 4 min read
- Email errors · EmailSPF PermError: too many DNS lookups (and how to fix it)SPF allows 10 DNS lookups. What counts toward the limit, how to count yours, and safe ways to get under it without breaking email.October 5, 2026 · 4 min read
- Uptime · SLAsWhat 99.9% uptime really means (with a downtime table)99.9% sounds close to perfect, but it allows 43 minutes of downtime a month. Here's what each common uptime target allows, why your real uptime is lower than any one provider's, and how to pick an SLA you can keep.October 2, 2026 · 5 min read
- Cron jobs · HeartbeatsHow to monitor cron jobs and catch the ones that silently stopCron jobs fail without telling anyone. Learn the heartbeat pattern: the job checks in when it finishes, and you get alerted when it doesn't, with examples for crontab, GitHub Actions and Kubernetes.October 2, 2026 · 5 min read
- TroubleshootingWebsite down? A 10-minute checklist to find the causeA calm, step-by-step way to find out why a site is down: is it really down, DNS, the certificate, the server, or the app. Each step takes a minute and says what to do next.October 2, 2026 · 5 min read