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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.

Image tools

Keep brand assets compliant before they reach the inbox

This section focuses on everything visual around BIMI. Before a mailbox ever displays your brand, the SVG logo must respect the Tiny-PS profile, stay lightweight and be delivered over a resilient HTTPS path. These tools proxy the assets through CaptainDNS, surface diagnostics and highlight the warning signs that would prevent display.

BIMI logo lookup

Download the SVG logo served by your BIMI record, analyse HTTP headers, redirects and size, and list the Tiny-PS findings reported by the backend engine.

Why audit BIMI logos ahead of time

Mail providers only render the BIMI logo when multiple conditions align: the record resolves, the SVG follows the Tiny-PS profile and the HTTPS endpoint behaves predictably. A logo that redirects across domains, serves an unexpected Content-Type or embeds unsupported features ends up ignored. By checking the asset proactively you avoid multi-day back and forth during a roll-out.

What the analyser reviews

  • Network delivery. Redirect count, latency, final URL and MIME type expose brittle CDN setups or missing HTTPS hardening. A slow or unstable path is flagged as a warning.
  • SVG structure. The backend parser reads the metadata, viewBox, declared width/height and raises diagnostics for forbidden tags, scripts, fonts or external references.
  • File weight. Oversized assets delay rendering in the mailbox. The analysis gives an immediate byte count to compare with BIMI recommendations (32 kB or less).

How to act on the report

  1. Fetch the logo once with the lookup tool. Keep the JSON output alongside your change tickets.
  2. Fix any blocking error first (unsupported tags, HTTP failures, non-HTTPS endpoints).
  3. Address warnings to improve resilience: simplify redirects, compress the SVG, document the final hosting location.
  4. Re-run the lookup to confirm the clean status before switching your BIMI record to production.