On one 34-line nodemailer digest sender it printed 15 findings (10 errors, 5 warnings) from 21 rules, each with file:line, the in-force date and the RFC or guideline it comes from.

Who it’s for
For developers and teams whose app sends email: receipts, digests, newsletters, password resets.

What breaks, and when
Since 2024-02-01 Gmail and Yahoo require SPF, DKIM, DMARC and one-click unsubscribe from bulk senders (5,000+ messages a day); mail that misses them is throttled or rejected.

What you get
• A scanner Claude runs over every .js/.ts/.py/.rb/.php/.tf/.yml/.zone/.eml file…
• 21 dated rules: SPF, DKIM, DMARC, BIMI, RFC 8058 one-click unsubscribe, TLS…

See it first
The real output of the bundled example is on getreadystack.com/skills/email-deliverability-check/ — free, no sign-up, so you see what it finds before you pay.

Install in 30 seconds
Unzip into ~/.claude/skills/, then ask Claude Code: “Why are our emails going to spam in Gmail? Check the repo. Don’t edit anything yet.”. Needs Node 16+.

What it does not do
No live DNS lookups, no test sends, no reputation or spam-rate data; it checks the records and code in your repo.

FAQ
Q: How is this different from asking Claude without the skill?
A: The skill carries a dated rule table and a scanner that reads every file, so Claude quotes the exact date and line instead of guessing from memory.
Q: How do I get the files?
A: In your Whop library after paying: the lesson “email-deliverability-check.zip”.