just technical issue. turn on internet id tracking, some are bogus (they send emails via other guys' internet service), in this case, save their email contents in a database, pick out those key words: for example, "ALERT", "OTC",..... then put those words into the anti-spamming software database, next time when they send you emails, the emails are automatically caught and trashed and you will not see them totally, those guys will try whatever they can, so need keep doing that, after a couple of weeks, your email system will not receive them totally.
in another case, i.e., their iternet site id is not bogus, then turn on the email blocking functions, trash those internet site id into the blocking list, next time any email from the blocked site will be automaticlly trashed and you will not find them totally.
I wrote a small program to fetch my emails, so I will reject all emails not in my recognized email list. if I find some suspecious emails, I use my program to send lots of bogus emails to them to fight back and try to crash them (but lots of time those guys use bogus internet id, so can not fight back).