DKIM Checker

A developer-focused tool to verify DKIM records, domain alignment, and signing algorithm, helping sysadmins ensure email authenticity and reduce deliverability issues.

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About This Tool

The DKIM Checker validates the public DKIM key published in DNS for a given selector and domain. It fetches the TXT record at selector._domainkey.domain, parses the DKIM1 tag set, and reports whether the required tags are present and well-formed. It focuses on the public key, the signing algorithm, and optional alignment with the From header to help operators diagnose misconfigurations before mail is sent.
Conceptually, the tool performs a DNS query, validates the key length and algorithm (default RSA-SHA256), and computes a verdict. If header_from_domain is provided, it checks domain alignment by comparing the d= value in the DKIM-Signature with the From domain. The results are structured and machine-readable to support automation and incident response.
Typical users include mail admins, security engineers, and DevOps teams integrating checks into deployment pipelines. Unique value lies in combining RFC6376-aligned validation with actionable remediation guidance and support for advanced options like DNS-over-HTTPS, multiple selectors, and explicit remediation tips.

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How to Use

Provide inputs: domain (e.g., example.org) and selector (e.g., mail).
Optionally provide header_from_domain to test alignment.
Choose canonicalization and signing algorithm (defaults apply).
Run the check to retrieve and analyze the DNS TXT record.
Review outputs: status, key_length, algorithm, alignment, and diagnostics.
If issues are detected, update the DNS TXT p value or selector and re-run.
Export results for reporting.

Frequently Asked Questions

Find Quick Answers

What is DKIM?

DKIM (DomainKeys Identified Mail) uses a cryptographic signature attached to outgoing emails. The signature is verified against a public key published in DNS, confirming the message originated from the claimed domain and was not altered in transit.

What does a valid DKIM check mean for deliverability?

A valid check indicates the public key is correctly published, the signing algorithm is supported, and alignment with the From domain is intact if tested. This reduces DMARC/SPF failures and improves mailbox trust and deliverability.

Why might the checker report a short or missing key?

Possible causes include a DNS TXT record with a too-short key, an incorrect selector/domain, truncated DNS responses, or misconfigured tags (p, k, or v). DNS propagation delays can also cause temporary invalid results.

Can I test multiple selectors or domains?

Yes. The tool supports separate checks per domain and selector. You can run multiple instances via automation or batch requests, with each result providing diagnostics for remediation.

Need to run multiple calculations?

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