Postfix Sign smtp from with DKIM

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Postfix Sign smtp from with DKIM

SysAdmin EM
Is it possible to sign smtp from with DKIM? I clarify that I am not talking about the header from.

I have installed opendkim and can only sign the header from.

What I am seeing is that some emails that I receive in the different Gmail tabs, for example Promotions, have a double dkim key:

Authentication-Results: mx.google.com;
       dkim=pass header.i=@stackoverflow.email header.s=s1 header.b=S0yxBc6Y;
       dkim=pass header.i=@sendgrid.info header.s=smtpapi header.b=uYee9Qd0;

The from address is stackoverflow.email but exits and second dkim from sendgrid.info.

My idea is to sign the email twice, but I don't understand how to do it. Does anyone use double signed?

Regards,
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Re: Postfix Sign smtp from with DKIM

Matus UHLAR - fantomas
On 27.03.20 10:46, SysAdmin EM wrote:
>Is it possible to sign smtp from with DKIM? I clarify that I am not talking
>about the header from.

no, only headers can be signed.
Also, that would make forwarding impossible. Don't try to do that.

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Re: Postfix Sign smtp from with DKIM

Ralph Seichter-2
* Matus UHLAR:

> On 27.03.20 10:46, SysAdmin EM wrote:
> > Is it possible to sign smtp from with DKIM? I clarify that
> > I am not talking about the header from.
>
> no, only headers can be signed.

Message headers and body, actually. You are of course right in that the
envelope data (SMTP session) is not DKIM signed.

-Ralph
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Re: Postfix Sign smtp from with DKIM

Wietse Venema
Ralph Seichter:

> * Matus UHLAR:
>
> > On 27.03.20 10:46, SysAdmin EM wrote:
> > > Is it possible to sign smtp from with DKIM? I clarify that
> > > I am not talking about the header from.
> >
> > no, only headers can be signed.
>
> Message headers and body, actually. You are of course right in that the
> envelope data (SMTP session) is not DKIM signed.

This is the main difference between DKIM (authenticates headers/body)
and SPF (authenticates SMTP MAIL FROM and SMTP client IP address).

        Wietse