DKIM record checker
Type a domain, and its DKIM selector if you know it, to find the public key receiving servers use to check your email's signature.
- No cost
- No sign-up
- No email
- No Google sign-in
- No subscription
- No limits for normal use
What is DKIM?
DKIM (DomainKeys Identified Mail) adds a digital signature to every email you send. Receiving servers check it against a public key published in your DNS, at selector._domainkey.yourbusiness.co.uk. If the signature matches, they know the email really came from you and wasn't changed on the way, which helps it reach the inbox and lets DMARC pass.
What is a DKIM selector?
The selector is the first part of the record's name, so a domain can have several keys at once – one per email service, or old and new keys during a change. Google Workspace uses google, Microsoft 365 uses selector1 and selector2, and other services choose their own. If you leave the selector blank, we try the common ones. To find yours for certain, open an email you sent, view the original message and look for s= in the DKIM-Signature header.
What the checker tests
- Whether the key exists under the selector, following any CNAME your provider asked you to add.
- Key type and size. 2048-bit RSA is the standard; 1024-bit still works but should be replaced, and anything smaller is rejected by many receivers.
- Revoked keys (an empty p=), which make every email signed with that selector fail.
- Testing mode (t=y), which asks receivers to go easy on failures.
Setting up DKIM
Switch it on in your email provider's admin panel (Google Workspace: Apps, Gmail, Authenticate email; Microsoft 365: the Defender portal). It gives you one or two records to add to your DNS. Do the same for every other service that sends email as you, such as newsletters and invoicing, then add a DMARC policy.
What it can't tell you
We can't list every selector a domain has: DNS doesn't allow it, so a key under an unusual selector won't show until you enter it. We check the published key, not whether a particular email was signed correctly.
Frequently asked questions
Is the DKIM checker free?
Yes. No sign-up, no email and no subscription, with only a fair-use limit to stop bots.
Why does it say no DKIM key found?
Your provider probably uses a selector we didn't try. Find it in the s= part of the DKIM-Signature header of an email you've sent, enter it and check again.
Should I use a 2048-bit key?
Yes. It's the current recommendation and every major provider supports it. Some DNS hosts need the long key split into two quoted strings, which is fine.
Do I need DKIM if I have SPF?
Yes. SPF breaks when email is forwarded, but a DKIM signature survives, and Gmail and Yahoo now expect both from bulk senders.
Related guides
SPF, DKIM and DMARC setup
Step-by-step SPF, DKIM and DMARC setup for Microsoft 365, Google Workspace and other email providers, with the exact records and how to test them free.
Why are my emails going to spam?
Why business emails land in spam: missing SPF, DKIM or DMARC records, a poor sender reputation or spammy content, with free checks and simple fixes.
Gmail, Yahoo and Microsoft sender rules
The sender rules Gmail, Yahoo and Outlook enforce: SPF, DKIM, DMARC, one-click unsubscribe and spam rates, in plain English for small businesses.
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