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I am signing all the emails for all domains that goes through my postfix MTA, but I need to custom sign some emails for some domain from my application, is it possible to stop opendkim from signing emails if it already has signature?

  • caz that emails wiil be signed the client's domain d tag will be client's domain, so currently their emails gets via mydomain.com in the head of the email! – Anil Bind Oct 5 at 7:17
  • I understand which emails you with to exclude from your own signing, but not why. Do you realize that multiple signatures, such as one from client and one from the service provider (you) are typically strictly value added? – anx Oct 5 at 20:09
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There might be a way with OpenDKIM but you can at least do it in postfix with header_checks.

Create /etc/postfix/header_checks with:

/^DKIM-Signature: / FILTER smtp:127.0.0.1:10025

Then in /etc/postfix/master.cf make two changes. First duplicate the SMTP listener so that it also listens on port 10025 but exclude the OpenDKIM milter. To the listen port, add the -o header_checks=regexp:/etc/postfix/header_checks option, e.g.

10025      inet  n       -       n       -       -       smtpd
smtp       inet  n       -       n       -       -       smtpd
        -o header_checks=regexp:/etc/postfix/header_checks
        -o smtpd_milters=inet:localhost:8891

Obviously change this to the submission port (587) and preserve any other flags, as appropriate to your situation.

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