Letterhead

Free tool

Check your email before your readers do.

Paste a sending domain to see whether SPF, DKIM and DMARC are in place. Or paste your email to get the checks Letterhead’s editor runs: bounce risk, links that won’t work, what an AI inbox reads, readability, and whether Gmail will cut it off at ~102KB. Free, no signup, and we don’t store what you paste.

We check the DKIM selectors Google Workspace, Microsoft 365 and the big email platforms use. If yours isn’t one of them, paste the full source of an email you sent, as it arrived (in Gmail: “Show original”), into “Check an email” and we’ll read it from there.

Know your DKIM selector?

It’s the s= value in an email’s DKIM-Signature header.

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.

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