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Developer DKIM Signing Validator & Canonicalization Lab

MTA Developer Toolkit

Debug your custom MTA implementation without sending test emails. Apply strict RFC 6376 canonicalization rules (relaxed/simple) to raw email components, visually inspect the pre-hash payload, and accurately compute the expected SHA-256 Body Hash (bh=).

Debug Your DKIM Implementation

Building a custom Mail Transfer Agent (MTA) or script? The #1 reason custom DKIM signatures fail is improper canonicalization before hashing. Paste your raw email components here to preview the canonicalized payload and generate the expected Body Hash (`bh=`).

Computation Complete

SHA-256

Expected Body Hash (bh=)

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Canonicalized Body Payload (Before Hashing)

This is the exact string passed to the SHA-256 algorithm after canonicalization rules were applied.

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Canonicalized Headers Payload

This is how the headers look right before being signed with the RSA private key.

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Processing Logs

The Ultimate Developer Toolkit

Designed specifically for engineers integrating DKIM. Stop guessing why your generated signatures are failing validation on the receiver's end.

Validate Canonicalization

Canonicalization (c=) is the hardest part of building a DKIM signer. Our engine applies strict RFC 6376 rules so you can compare our output string with yours.

Generate Body Hashes (bh=)

We automatically strip trailing empty lines and reduce whitespace (if relaxed) to compute the exact Base64 SHA-256 hash your email body should produce.

Header Unfolding

Emails often fold long headers across multiple lines. Our engine properly unfolds them and lowercases the keys (in relaxed mode) exactly as receiving servers do.

CRLF Normalization

Different operating systems use different line endings (\n vs \r\n). Our tool enforces strict network line endings before processing the cryptographic hash.

Visual Payload Inspection

See exactly what the hashing function "sees". By looking at the raw canonicalized payload, you can easily spot if your code is missing a crucial line break.

Local Dev Companion

No need to send test emails to Gmail just to see if they bounce. Validate your signing parameters offline, directly during your development cycle.

Done!

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Developer DKIM Signing Validator & Canonicalization Lab

Debug Your DKIM Implementation

The Ultimate Developer Toolkit

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