Thank you for the praise.

I have taken a look at your request. It would certainly be possible in principle. The difficulty for me at the moment is setting up such an infrastructure at my place so that I can test the implementation. I also face the problem of having to provide support for the activation of DKIM at the user's mail provider if someone wants to use this function as well. Of course, your request is justified for the time being and will remain open. Personally, however, I will first have to read up on this further. Perhaps it will be implemented via a pull request.