The spammers have been busy. They figured out they can bypass most ISP SPAM filters by adding the header
<on behalf of>
which doesn't get flagged by the majority of filter programs, devices or client application settings.
Filters look at the "from" address after the "on behalf of" header, which means the filter overlooks the actual "from" address:
FROM: SOME SPAM ADDRESS on behalf of SOME ADDRESS THAT ISN'T BEING FILTERED.
If you're using MS Outlook, though, you can filter for the spam "from address" strings.
Create a rule in Outlook that looks for the offending string (.pro, .promo4u, etc.) and select "ANY HEADER" and "CONTAINS" for the filter parameters.
You'll have to add more to the list of strings to filter, and it has to be enabled on all your Outlook devices.
Hoping the ISPs get around to implementing the same for their incoming mail filters.