suggesting new ways to fortify email blocking

You can do that with Rules in the Mail app:

I use it all the time. Even when I get spam from Russia I add a couple of cryptic alphabet characters in the Message Content contains filed. Since I don't expect any email ever from Russia I added

Well, it is a real-word tool that I use, because I was getting about 20 SPAM emails per day from nearly a dozen different themed sources, but their Mail header Return-Path narrowed all this crap down to two servers.

If you click that first button in my previous screen shot from the Edit Rules dialog, there will be a long list of possible choices, but no Return-Path. At the very bottom of that list, is an Edit Header List… entry. Click that, and literally add Return-Path as typed here. When you select a SPAM email message, and then visit your Rule, when you enter Return-Path, and select contains, the actual Return-Path server address automatically fills in for you. When you save the rule, it will prompt you to apply the rule, and when you do, the SPAM is toast.

You might get 20 SPAM emails from different addresses and servers, but they may all be using one or two Return-Path servers. The Mail rules allow you to add extra Mail header fields, and base your filtering on the server address in the Return-Path. Then you use a Mail rule to filter these like this:

and then move the message(s) to the Trash.

Eventually, Return-Path Mail servers are changed, though infrequently. I have had to change those associated with the original SPAM 20 once in 12 months. Apple is not in the Mail rule writing business, and they just provide the tools that end users can choose from to create their own custom rules. Admittedly, it is a low documentation subject.

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