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Email Proteccion: DKIM Broken on forwarding email.

Alejandro Sanchez over 4 years ago

I have a self hosted mail server which has DKIM implemented.

When an account in the internal mail server has a forward configured, the DKIM for that email breaks.

For example:

Internal account: test@tuaiti.com.ar. Forwards all incoming email to test@gmail.com

UTM receives the mail for test@tuaiti.com.ar and forwards it to the internal mail server.

The mail server receives it, complains about the dkim imformation, and forward to test@gmail.com
Gmail receives the email and complains about security, because of the failed DKIM test.

I believe that i'm missing some configuration in the UTM.

Thank you.

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0 Alejandro Sanchez over 4 years ago

I tested disabling DKIM on the internal server and using this https://community.sophos.com/kb/en-us/115300 to configure DKIM on the UTM.

Same results.
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0 BAlfson over 4 years ago in reply to Alejandro Sanchez

Hola Alejandro and welcome to the UTM Community!

I agree that you should disable DKIM in your mail server and use the SMTP Proxy to add the DKIM tag. Please show a picture of the DKIM configuration in the UTM. Also, copy the SMTP log lines here related to one such email.

How does your setup differ from Basic Exchange setup with SMTP Proxy.

Cheers - Bob

Sophos UTM Community Moderator
Sophos Certified Architect - UTM
Sophos Certified Engineer - XG
Gold Solution Partner since 2005

MediaSoft, Inc. USA
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+1 DouglasFoster over 4 years ago in reply to Alejandro Sanchez

If you have a policy that adds standard headers or footers to a message, or alters the subject line, all of this must be completed before the DKIM signature is applied.
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0 Alejandro Sanchez over 4 years ago in reply to DouglasFoster

Thank you, this was the problem. I disabled the "Malware check footer" and now everything is working again.

I think the problem is because I have DKIM on the internal mail server and not in the UTM.
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