It can be overwhelming, but I wouldn't reply to remove your email. That let's them know your email is active and it could be sold or emailed out to more services or somewhere else. (if the original email is even from a firm and not a mailing list) I just tag it as junk mail and delete my folders at the end of the day. I only get like 2/day if that now, so it's really worked for me to tag em.
There are times they have their uses...I will give them that, but honestly it is very few and VERY far between.
There are a few of them that I believe are legitimate, and I have worked with 1 or 2 of these companies, but you are right...the majority are flesh-peddling wastes of time.
I don't have a solution...just a sympathetic reply as I think we all deal with this same issue.