Free tool · DKIM checker
Free DKIM checker
Type your sending domain and we look for a DKIM key at the selectors Google Workspace, Microsoft 365 and the big email platforms use. Don’t know your selector? Paste an email you sent, as it arrived, into Check an email and we read it from the signature. Free, no signup.
About DKIM
What DKIM does
DKIM adds a signature to every message you send. Receivers fetch your public key from DNS and use it to check that the message really came from your domain and wasn’t changed on the way.
The key lives at selector._domainkey.yourdomain.com. The selector is a label your email platform picks, which is why most DKIM checkers can’t help until you tell them what it is.
How to find your selector
- Open a newsletter you sent, in Gmail.
- Open the three-dot menu and choose Show original.
- Find the
DKIM-Signatureheader. The selector is thes=value, and the signing domain isd=.
Or skip the hunting: copy the whole original into Check an email above, and we read the selector and offer to check your domain with it.
When you change platforms
Each sending service signs with its own selector and key. When you move your newsletter, publish the new platform’s DKIM record before your first send, and leave the old one up until the last send from the old platform.
In Letterhead, these checks run while you write.
Every issue gets a content check before it goes out: bounce risk, links that won’t work, what an AI inbox will read, readability, and email weight with what’s making it heavy. Letterhead also strips redundant styling from what it sends, so your newsletter goes out lighter than you wrote it.
| The old way | In Letterhead |
|---|---|
| Find out Gmail clipped you when a reader asks where the unsubscribe link went. | Email Weight shows how heavy every issue is, and what’s making it heavy, before you send. |
| Click every link by hand the morning of the send. | Links with no working destination are flagged in the editor before you send. |
| Paste the HTML into another tool to slim it down. | Letterhead strips redundant styling from what it sends, so it goes out lighter than you wrote it. |
FAQ
Questions about DKIM
What is a DKIM selector?
A label that tells receivers where to find your public key: they look it up at selector._domainkey.yourdomain.com. It’s the s= value in a message’s DKIM-Signature header.
Why can’t the checker find my DKIM key?
We check the selectors the common platforms use. If yours uses its own, paste a received copy of your newsletter into Check an email and we’ll find it, or type the selector under “Know your DKIM selector?”.
Can a domain have more than one DKIM key?
Yes. Each selector is its own record, so Google Workspace, your newsletter platform and your CRM can each sign with their own key.
Do I need DKIM if I have SPF?
Yes. Gmail and Yahoo expect both from bulk senders, and DKIM survives forwarding, where SPF often breaks.
Do you keep the domain or email I check?
No. We don’t store what you paste or the domain you look up.
The Letterhead Brief
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The Brief lands once a week. Want these checks running on your own newsletter? Book a test drive →