Hey fellow self-horders!
I built mailcheck — a free, open-source tool that checks all 6 email authentication protocols (SPF, DKIM, DMARC, MTA-STS, TLS-RPT, BIMI) for any domain and gives you a 0–100 deliverability score.
Try it: https://korpo.pro/ — type any domain and get instant results.
Self-host it: It’s MIT licensed with a FastAPI backend. pip install mailcheck or clone from our Forgejo repo.
CLI: mailcheck example.com — great for CI/CD integration (exit code 2 on critical issues).
API: curl https://korpo.pro/api/v1/check/example.com — no auth needed, 100 req/hr.
Batch mode: mailcheck --file domains.txt
I found that many well-known domains have misconfigurations — even big crypto projects. The tool helped me fix my own domain’s email auth setup.
Would love feedback from email/infra folks!
The problem with tools like this is that they don’t actually check that the mail is sent correctly. You can define security keys, but they don’t mean anything if your mail server doesn’t use them correctly.
For testing, I use https://www.mail-tester.com/ which you send an email to and it does more thorough tests on the server and email itself.
Yeah and I’m not seeing any mention of blocklist checking. I was sending email for months with no issue then the ISP apparently updated their PBL.