321 stars · Apache-2.0 · 6.0.1 (2026-09-04)
Checks a domain's SPF, DKIM, DMARC and MTA-STS records in seconds — whether the newsletter you have not built yet is even allowed to arrive.
▶Repo detailsthe review · specs · pros & cons · install
What it is
A small Python command-line tool and library that reads a domain's DNS records — SPF, DKIM, DMARC, MTA-STS, plus the mail servers themselves — and reports, in plain language, what is missing or broken. You give it a domain name; it gives you a report you can act on.
Why it matters
Listmonk has been sitting at the top of your email plans since Edition 2, and Edition 2 was explicit that Listmonk does not send mail — you need SES or Postmark plus correct SPF, DKIM and DMARC records. Almost nobody sets those up correctly the first time, and the failure mode is silent: your campaign sends, the dashboard says 100% delivered, and a large share of it lands in spam where you will never see it. Gmail and Yahoo now reject bulk mail outright from domains with no DMARC record, so this is not a nicety. Ten minutes with this tool, before you write a single newsletter, is the difference between building an audience and building a list of addresses that never hear from you.
- Runs in seconds against a domain you do not control, so you can check your own and then check three competitors' to see what good looks like.
- Output is JSON as well as text, so a nightly Procrastinate job can shout at you if a record ever changes or expires.
- Explains what each failure means rather than just printing a red cross — genuinely readable if you have never touched a DNS record.
- It diagnoses; it does not fix. The actual repair is editing DNS records at your registrar, which is fiddly, slow to propagate, and easy to get subtly wrong.
- Correct records are necessary but not sufficient — reputation, list hygiene and content still decide whether you reach the inbox.
- 317 stars and effectively one maintainer. It is a tool to run occasionally, not a dependency to build a product on.
Standalone tool, run from your Mac.