RunStack Checks

Resolve a name at several public resolvers (Google, Cloudflare, Quad9, …) and compare their answers. Use after changing DNS records to check propagation, or when some users reach a different IP or get NXDOMAIN. Use check_email_domain instead for SPF/DKIM/DMARC analysis. Returns per-resolver answers, inconsistencies and a verdict.

Check whether an IP address or a domain is on email blocklists (DNSBL/RBL): Spamhaus ZEN and DBL, SpamCop, Barracuda, UCEPROTECT, Mailspike, SURBL, URIBL and others. For a domain, its own name is checked on domain lists and its A/AAAA addresses on IP lists. Use when mail bounces with 'listed'/'blocked' errors or lands in spam, or after a server was compromised. Lists that refuse queries from public resolvers are reported as not tested, never as listed. Returns listed lists with the reason and a delisting link. For SPF/DKIM/DMARC use check_email_domain.

Look up a domain's registration in the registry (RDAP, or WHOIS for .ru/.su/.рф): expiry date and days left, registrar, creation date, EPP status codes (clientHold, redemptionPeriod, transfer locks…) with explanations, nameservers and DNSSEC. Use to check when a domain must be renewed or why it suddenly stopped resolving. Subdomains are reduced to the registered domain. For DNS records use check_dns.

Audit a mail domain as other mail servers see it: MX, SPF (including the 10-DNS-lookup limit), DKIM, DMARC policy, PTR / forward-confirmed reverse DNS, SMTP STARTTLS on the MX hosts, MTA-STS, TLS-RPT, BIMI. Use when mail lands in spam or bounces, after changing mail provider or DNS, or before tightening DMARC. Use this (not check_dns) for any email deliverability or authentication question. Returns a verdict, findings with cause and fix, and a report link.

Request a public URL from outside your network and inspect the HTTP layer: status code, full redirect chain, security headers (HSTS, CSP, X-Frame-Options, X-Content-Type-Options, Referrer-Policy…), caching and compression headers. Use to debug redirect loops, unexpected status codes or missing headers as real visitors and CDNs see them, or to verify a web server / CDN config change after deploy. Use check_tls instead for certificate or TLS protocol questions. Returns a verdict and findings with fixes.

Look up an IP address or ASN: owner organization, announced prefix, PTR (reverse DNS), RPKI validity and geolocation. Use to identify who is behind an address seen in logs or headers, or to check PTR / RPKI for a mail or BGP issue. Does not test reachability (use check_port).

Check from the internet whether TCP ports of a public host are open, closed or filtered. Use to verify firewall / security group rules, or to find out why a service works locally but is unreachable from outside. Only public addresses are accepted; this does not test the application behind the port (use check_http or check_tls for that).

Scan a public host's TLS from the internet: certificate validity, chain completeness, expiry date, hostname match, enabled protocols (TLS 1.0–1.3), cipher suites, HSTS. Use when browsers show certificate errors, before/after renewing or rotating a certificate, or to confirm old TLS versions are disabled. Use this (not check_http) for anything about the certificate or TLS configuration itself; works on any TLS port, not only 443. Returns a verdict, findings with cause and fix, and a shareable report link. Takes up to ~60 s.