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CaptainDNS

Propagation & diagnostics

Compare resolvers worldwide and inspect returned answers.

Email authentication

Tools to verify and validate your email authentication setup.

SPF syntax validator

Review include chains and DNS query limits before publishing changes.

SPF record inspector

Resolve the published TXT record, flag lookup limits and decode each mechanism.

DKIM syntax validator

Quickly check the syntax of your DKIM records.

DKIM record check

Resolve a selector and analyse the published DKIM TXT record.

DMARC syntax validator

Check rua/ruf destinations, alignment modes and the active policy before publishing.

DMARC record inspector

Resolve the published policy, surface diagnostics and confirm enforcement before switching to reject.

BIMI syntax validator

Validate BIMI tags, the logo fetch and the VMC certificate before publishing.

BIMI record inspector

Resolve the published BIMI record, inspect logo and VMC diagnostics in one place.

Email deliverability audit

Audit MX, SPF, DKIM and DMARC to confirm a domain is ready to send.

Mail header analyzer

Decode participants, authentication results and routing from raw headers.

DMARC record generator

Create compliant DMARC records with all policy and reporting options.

Text

Transform, encode and measure your content in seconds.

Text case converter

Convert any block of text to upper or lower case instantly.

Base64 encoder / decoder

Encode or decode any content in Base64 without leaving the browser.

Slug generator

Transform any sentence into an SEO-friendly slug in seconds.

Word & character counter

Measure the length of any text, with instant word and character counts.

Images

Preview and validate your BIMI logos before publishing.

BIMI logo lookup

Inspect a BIMI logo URL—format, metadata and live rendering—before rollout.

Certificates

Inspect CSRs, BIMI logos and VMC certificates before you deploy.

CSR parser

Inspect a CSR, extract subject details, fingerprints and requested SANs.

VMC inspector

Inspect a Verified Mark Certificate—issuer, validity and SAN coverage—before you publish BIMI.

IP

Look up addresses, owners, reverse records and ranges.

Reverse lookup

Resolve a PTR record and validate DNS consistency.

IP WhoIs

Identify the owner of an IP range and its contacts.

IPv4 netmask

Calculate network, broadcast and usable hosts for any IPv4 block.

My IP address

Detect your IPv4/IPv6 addresses and their geolocation.

BIMI logo lookup

Check HTTP delivery, weight and Tiny-PS compliance in seconds

Paste the URL exposed in your BIMI record to validate the SVG asset without leaving the browser. CaptainDNS proxies the download, measures latency, records redirects and runs the Tiny-PS checks used by the backend resolver.

What the lookup returns

  • HTTP metrics. Observe latency, number of redirects, final URL and reported MIME type to catch fragile hosting or missing HTTPS hardening.
  • SVG metadata. Title, viewBox, width/height attributes and additional tags help document the asset and confirm the Tiny-PS profile.
  • Diagnostics. Errors stop the logo from rendering. Warnings highlight risky constructs (external references, scripts, oversized files) that mailbox providers may reject.
  1. Copy the l= URL from your BIMI TXT record and launch the lookup.
  2. Export the JSON response to keep an audit trail with your change request.
  3. Fix blocking errors first (invalid HTTPS endpoint, missing Tiny-PS requirements, parsing failures).
  4. Address warnings: simplify redirect chains, reduce the file size, document the final CDN location.
  5. Re-run the lookup until the status is clean, then publish or update your BIMI record.

Good practices when hosting BIMI logos

  • Serve the SVG over HTTPS with a predictable CDN or origin that supports caching and redirects sparingly.
  • Keep the file below 32 kB, remove unused metadata and make sure the viewBox matches the intended display.
  • Avoid scripts, fonts, foreignObject and external references: they violate Tiny-PS and are blocked by mailbox providers.
  • Monitor latency over time; sudden spikes usually signal CDN incidents or expired TLS chains that will prevent the logo from loading.