this post was submitted on 26 Apr 2026
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Selfhosted

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38
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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[–] savvywolf@pawb.social 10 points 1 month ago (1 children)

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.

[–] 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.

[–] ikidd@lemmy.dbzer0.com 5 points 1 month ago

Yah, I don't think this is working. It's failing spf and dkim records that have worked for years

[–] wilo108@lemmy.ml 3 points 1 month ago

Shows a failure if the DKIM selector isn't on an arbitrary list? What's going on there?

[–] pHr34kY@lemmy.world 3 points 1 month ago

Interesting. I'm getting full marks on mxtoolbox but failing the same tests on this one.

[–] irmadlad@lemmy.world 2 points 1 month ago

Firefox 149.0.2 (64-bit), Linux Mint, using VPN. I must have settings that are blocking the processing of the domain for whatever reason. I've tried multiple domains including well known domains. No joy. Sorry about that.

[–] Decronym@lemmy.decronym.xyz 1 points 1 month ago* (last edited 1 month ago)

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters More Letters
SSL Secure Sockets Layer, for transparent encryption
TLS Transport Layer Security, supersedes SSL
VPN Virtual Private Network

1 acronyms in this thread; the most compressed thread commented on today has 6 acronyms.

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