kumomta/docs/reference/message/dkim_verify.md

message:dkim_verify()

{{since('2023.11.28-b5252a41')}}

This method will verify each DKIM signature that is present at the top level of the message, up to a limit of 10 signatures. The limit is in place to limit the scope of a DoS attack being carried out through maliciously constructed messages.

For each signature, an authenticationresult object will be constructed and an array of those results will be returned to the caller.

Example: obtaining DKIM authentication results

kumo.on('smtp_server_message_received', function(msg)
  -- Verify the dkim signature and return the results.
  -- Note that this example isn't making any policy decisions;
  -- it is only annotating the message with the results and
  -- allowing it to be relayed
  local verify = msg:dkim_verify()
  print('dkim', kumo.json_encode_pretty(verify))
  -- Add the results to the message
  msg:add_authentication_results(msg:get_meta 'hostname', verify)
end)

might print something like this to the diagnostic log:

dkim    [
  {
    "props": {
      "header.d": "github.com",
      "header.i": "@github.com",
      "header.s": "pf2023",
      "header.a": "rsa-sha256",
      "header.b": "jo0EO4dX"
    },
    "result": "pass",
    "method": "dkim",
    "reason": null,
    "method_version": null
  }
]

and produce an Authentication-Results header:

Authentication-Results: hostname.example.com;
        dkim=pass
        header.a=rsa-sha256
        header.b=jo0EO4dX
        header.d=github.com
        header.i=@github.com
        header.s=pf2023

See Also:

• msg:add_authentication_results()