this post was submitted on 26 Apr 2026
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Selfhosted

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Mailcheck – Free/open-source email deliverability checker (SPF, DKIM, DMARC, MTA-STS, TLS-RPT, BIMI) (korpo.pro)
submitted 1 month ago by mailcheck@lemmy.dbzer0.com to c/selfhosted@lemmy.world
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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!

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[–] Dultas@lemmy.world 1 points 1 month ago

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.