SNIP...
some questions...
- what puts our dkim-signature into the headers? and when?
- what decides if the dkim signature should be included and how?
- what does sqpsmtpd do?
- who deals with aliases, groups, forwarding,vacation messages etc etc?
I commend you for this post. It can only help.
I am no expert and probably a bit dangerous in posting a reply. Lack of wisdom never stopped me before, sooo...
1. DKIM is defined in the DNS zone record. The topic is complicated, but it boils down to updating your zone record with a properly formatted string. The devil is in the details.
2. I don't know, but I am going to take a look around.
3. sqpsmtpd handles secure smtp negotiations. It recieves the request from your client to send an email, then verifies that you can or not.
4. The system admin. You can add various contribs to provide convenience features, such as allowing the system user to set their own password, vacation message, and so on.
I hope this helps a bit. Please post more questions in this thread. It may be a great way to gather info to update the documentation.