New tools
MTA-STS & BIMI hosting, TLS-RPT monitoring
CaptainDNS hosts your MTA-STS policy and BIMI logo, and monitors your TLS-RPT reports automatically. All free, no server required.
Google, Yahoo and Microsoft now require stronger email authentication. Protect your deliverability in just a few clicks.
MTA-STS guides and tutorials: secure email transport with mandatory TLS encryption.
8 articles
Step-by-step tutorial to deploy MTA-STS on Microsoft 365, Google Workspace, and Cloudflare. MX patterns, policy file, hosting, and validation included.
DNS Lookup
Choose a DNS record type to search for.
Propagation & diagnostics
Compare resolvers worldwide and inspect returned answers.
Keep history, monitor your zones and automate recurring checks.
Email authentication
Tools to verify and validate your email authentication setup.
Deliverability
IP tools
Quickly inspect an IP address or your own connection.
My IP address
Detect your IPv4/IPv6 addresses and their geolocation.
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.
IPv6 subnet calculator
Calculate IPv6 subnets, address ranges and reverse DNS entries.
Text
Transform and measure your content in seconds.
Text case converter
Convert any block of text to upper or lower case instantly.
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.
Password generator
Generate strong random passwords and memorable passphrases instantly.
Developer
Encoding, hashing, regex and formatting for everyday dev work.
Base64 encoder / decoder
Encode or decode any content in Base64 without leaving the browser.
Hash Generator
Compute MD5, SHA-1, SHA-256 and SHA-512 hashes of any text.
URL encoder / decoder
Encode or decode text using percent-encoding (RFC 3986) right in your browser.
Regex Tester
Test a regular expression against text and visualize matches.
JSON / YAML Formatter
Format, validate and convert JSON and YAML in one click.
Web & Certificates
BIMI logos, VMC/CSR certificates and web page diagnostics.
BIMI logo lookup
Inspect a BIMI logo URL - format, metadata and live rendering - before rollout.
BIMI SVG converter
Convert any SVG to BIMI-compliant Tiny-PS format in seconds.
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.
Page size checker
Check if your page exceeds Google's 2 MB crawl limit.
Phishing URL Checker
Check if a URL is flagged as phishing or malware by 4 threat intelligence sources.
