OK, I have something that follows these requirements (except the site-defaults + site-config thing, currently site-wide checks take precedence). If you want to look at it : https://gitlab.com/abompard/mailman/commits/import-header-matches
If you have some time Barry, I'd like your review on some things that I'm not sure I'm doing right: In the code and in the tests, I'm importing the new model object, HeaderMatch. Is it OK? Should I go through the corresponding interface instead? It looks like models are almost never imported from throughout the code (except in the model module), and I don't know if that's a best practice that should be followed here. If it is and you have details on the reasoning, I'm interested :-) Example : https://gitlab.com/abompard/mailman/commit/7a14a5f42af35185bee19b8e09c6e272f...
Thanks ! Aurélien