Show HN: DMARC Checker

[akshayKMR]

Hey, this comes at a perfect time for me.

I had posted my app on Betalist about a week ago and received a vulnerability report about incorrectly configured DMARC from a security researcher. I made the fix but wasn't confident about it. Shortly after, I received a couple more similar emails.

With this tool, my first check failed, citing an invalid SPF record. (I had an extra `.` at the end of my TXT record). Now, the check shows all passing.

I hope all is good now (emails are wild).

From my limited understanding:

    SPF <- Should this server be sending emails for this domain?
    DKIM <- Was this email tampered with?
    DMARC <- What should I, as a recipient, do if SPF or DKIM fails?

Thanks!

[awulf]

I'm really happy to read that the app was able to help! Thanks for sharing.

[1231232131231]

DMARC itself contains some extra checks (alignment check).

[bks]

Great tool, one bit of feedback on the log report. Perhaps you can highlight the passing line in the SPF record, I have about 100 of these "The ip4 mechanism does not match." and then a lot of "The include mechanism matches and produces a pass result."

Maybe you can highlight the passing statement? - https://app.screencast.com/Hu5ybB6K3fd9R

[awulf]

Thanks for the feedback, much appreciated! It looks like you've flattened your SPF record, causing a large number of log messages. I'll see what I can do to better highlight the line that produces the 'pass' result.

[jenoer]

I don’t want to take away your spotlight, because it’s a nice project you launched,

But I do want to point out to people that https://github.com/domainaware/checkdmarc exists for quite a while. I use it often and have also integrated it in various automated tooling.

(It also does not require handing out email addresses to strangers.)

[petecog]

I've given it a go.

I recommend also https://mxtoolbox.com/dmarc.aspx

I have no affiliation.

[petecog]

Great tool. Good comprehensive report. Keep up the great work. Hope it helps people.

Email is such an amazing mess. Love and hate in equal measures

[bks]

Seems that this tool actually validates your email and checks its alignment vs. just checking to see if there is a dmarc record on the domain.

[yolo4553]

Hmm, am I seeing this correctly that the system does receive emails only via IPv4 and no IPv6? This would make the SPF check somewhat misleading as it only checks one option.

[awulf]

You are correct, the mail server is currently configured to only receive emails via IPv4. This setup is not uncommon as most major email providers have IPv4-only MX records (with Gmail and Yandex Mail being rare exceptions that support IPv6).

It might be a good idea to provide a different email address whose mail server explicitly requires IPv6. I'll think about it. Thanks for bringing it up.

[ollybee]

This seems similar to https://www.mail-tester.com which I use all the time to quickly diagnose mail issues

[aeadio]

A simple reject policy is showing up as an error, despite validating fine with other DMARC checker apps like MX Toolbox,

    The From domain (...) has an invalid DMARC record.
    ...
    DMARC record found: v=DMARC1; p=reject;
    The DMARC check result is permerror.

No explanation as to what permerror means.

It might also be useful if the tool attempted to circumvent DNS caching, so users can try tests in succession after updating.

[awulf]

There was a small bug in our DMARC record parser (it didn't like the semicolon at the end of the record). Sorry for that. Your DMARC record is definitely correct. The issue should be fixed now.

Also, thanks for the idea about circumventing DNS caching. I'll look into adding that feature.

[RulerOf]

This is a really straightforward tool. Validating spf/dkim/dmarc by receiving an email strikes me as more effective than something that just looks at the DNS records. Thanks for sharing.

[bks]

Also check out - https://appmaildev.com/en/dkim

[kunley]

Handy tool and looks better than a few similar I tried. Thank you!

[FerretFred]

Hey this is great! Just woken up, sipping tea in bed and have now got a fully validated DKIM/SPF setup. So easy... thank you!

[wilg]

Very cool, thanks!