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Email deliverability preflight checker

Parses a raw email or split headers, HTML and plain text, then checks sender alignment, List-Unsubscribe headers, message size, image to text ratio, link domains and the plain-text part against sender guidelines.
Raw message source

Alignment is judged from header and link domains only: nothing here queries DNS, so SPF, DKIM validity, and DMARC policy are not checked. Run those record checks with your DNS provider or a lookup tool before a big send. MIME bodies are not decoded either, so a Base64 or quoted-printable raw source is scanned as pasted; the split headers-and-content mode sidesteps that. The requirement checks mirror the Google and Yahoo bulk sender rules (one-click List-Unsubscribe headers, aligned sending domains); the rest is advice, and a pass here is not a deliverability guarantee.
Options

More web & auth tools

- HTTP header parser (/web/headers)
- Cookie analyzer (/web/cookie)
- URL encoder (/encoding/url-encoder)
All web & auth tools (/web)

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Canonical HTML: https://nutter.tools/web/email-deliverability-preflight-checker
Markdown version: https://nutter.tools/web/email-deliverability-preflight-checker.md
Plain-text version: https://nutter.tools/web/email-deliverability-preflight-checker.txt
Agent index: https://nutter.tools/llms.txt