DKIM Test

This tool tests your DomainKeys Identified Mail (DKIM) setup. You send a test email to a generated address and get as result, whether the email contains a valid DKIM signature. Additionally, the tool checks the DKIM signature for identifier alignment to the sender From domain as required by DMARC.

Test Method

Test results can be retrieved later by entering the email address generated for the test. If you send multiple emails to the same test address, only the first one will be evaluated and shown. Results will be purged after 24 to 48 hours. The test will yield no result if the email is rejected by my MTA on SMTP level, e.g. due to an invalid sender address.

The test will be successful if any DKIM-Signature in the email is verified correctly and the email passes identifier alignment. The test uses the dkimpy library for DKIM verification as shipped by Debian in package python3-dkim. When testing with dkimpy by yourself, beware that by default it verifies the topmost DKIM-Signature occurrence only.

The identifier alignment used in the test is not part of the DKIM specification (RFC6376); an email may pass the DKIM validation, even if the identifier is misaligned. The identifier alignment is required by DMARC (RFC7489). The test assumes DMARC “strict mode”, i.e. requires the RFC5322 From domain to exactly match the DKIM d= field. However, the test does not attempt DMARC validation.

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