CaptainDNS : MX, SPF & DMARC Checker

One click shows the MX, SPF and DMARC records of the site you are on. DNS lookups go to Cloudflare, nothing to CaptainDNS.

Click the CaptainDNS icon and see whether the domain of the site you are on receives mail and protects the mail it sends. What the popup shows The extension takes the host name of the site in the active tab, walks up to the root domain (www.example.com gives example.com; so does app.example.com, unless app has its own DNS zone) and reads three DNS records: • MX, the servers that receive mail for the domain; • SPF, the servers allowed to send on its behalf; • DMARC, the instruction given to mailbox providers for messages that fail. Each line gets a color from fixed rules. SPF: green for ~all or -all, orange for ?all or no all, red when missing, duplicated or +all. DMARC: green for quarantine or reject, orange for p=none, red when missing, duplicated, without p= or with an unknown p=. MX: green when at least one server is published, orange when there is no MX or when a Null MX is mixed with other MX records, grey for a Null MX alone (a domain that refuses mail). Limits The extension does not ship the Public Suffix List. A subdomain with its own DNS zone is checked as is (app.example.com, not example.com). On a site hosted under a platform domain, such as user.github.io or project.vercel.app, the popup shows the records of github.io or vercel.app, not those of the site. Going further DKIM, MTA-STS, BIMI and blocklists need more queries than a popup should send. The "Open the full audit" button opens the CaptainDNS audit page with the domain already filled in. Privacy • A single permission: activeTab. The extension reads the tab address when you click its icon, never in the background. • The site's full host name (subdomains included, e.g. staging.example.com; never the page path) is sent to Cloudflare's public resolver (1.1.1.1, DNS over HTTPS) for DNS resolution. Cloudflare also sees your IP address, as with any network request. • Nothing is sent to CaptainDNS unless you open the full audit. No telemetry, no account, no storage. • Plain, unminified JavaScript that can be read as is. Details and privacy policy: https://www.captaindns.com/en/browser-extension#privacy Publisher: ESPIERRE SAS, Paris. Works on Chrome, Microsoft Edge and Firefox 140 or later. Interface in English and French.