What can the email header parser do?

Paste the raw email header (Received/DKIM-Signature/Authentication-Results etc.) to extract the mail path, authentication results and delivery delays, helping diagnose why mail is rejected or lands in spam.

How do I use the DNSBL lookup?

Enter a sending server IP or domain to check its listing status across 21 major DNSBLs such as Spamhaus, Barracuda and UCEPROTECT (IP queries automatically match IP lists; domain queries match domain/URI lists). A blacklisted IP causes bulk mail rejection; you must file a delisting request with the relevant organization.

What does the SMTP error code reference cover?

Covers 2xx success, 4xx temporary failure (e.g. 450/451/452) and 5xx permanent failure (e.g. 550/552/553/554) with full meanings and remediation advice to quickly pinpoint bounce causes.

What is the CIDR calculator for?

Converts IP addresses and subnet masks to CIDR notation and computes usable host counts. Commonly used to plan ip4: segments in SPF records and mail server IP ranges.

🔧 Email Toolbox

Pure frontend · Zero backend · Real-time DNS lookup via DoH

🩺 DNS Comprehensive Diagnostic Tool

One-click check of MX, SPF, DKIM, DMARC, PTR, BIMI, MTA-STS, TLS-RPT, DNSSEC

→ Go to DNS Diagnostic Tool

📧 Email Header Parser

Paste the raw email header to parse the Received hop chain, Authentication-Results, DKIM-Signature and ARC info

⏳ Parsing...

🚫 DNSBL Blacklist Lookup

Enter an IP address or domain to check its status on major DNSBLs in real time

⏳ Querying blacklists...

🔢 SMTP Error Code Reference

Common SMTP 4xx/5xx error codes: meanings, causes and fixes

📡 SPF Deep Validation

Query and deeply parse SPF records: mechanism coverage, 10-DNS-lookup limit warning, include recursion tracking

⏳ Querying SPF record...

🔑 DKIM Record Checker

Query and parse DKIM public key records: key type, length, algorithm audit

⏳ Querying DKIM record...

🛡️ DMARC Analyzer

Query the _dmarc TXT record, parse policy tags and interpret current protection status

⏳ Querying DMARC record...

🔐 Base64 / Quoted-Printable Encode / Decode

Email MIME content encode/decode tool

🌐 CIDR Calculator

IP range calculation, CIDR aggregation, SPF range conversion

✉️ Email Address Syntax Validator

RFC 5321/5322 compliance check with flagged issues

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