All that you can do, really, is just to keep deleting them. As advances are made to stop spam e-mail, the spammers will change their tactics to avoid whatever is blocking them.
I have a company, like your stock company, that sends me several e-mails every day, and, for each one, the place of origin is different. So, if I place one point of origin on my spam-blocking list, it doesn't matter, because each new e-mail apparently/seemingly comes from a different location.
Spam e-mail in my computer inbox is much like the "junk mail" that ends up landing in my paper mailbox: Not too much that can be done to stop either of them, though both are only a waste of my time....
GeoThorn