Quora seems especially bad about this too. You search for something, and then Quora takes that as an invitation to send you a bunch of spam. To make it worse,

Quora seems especially bad about this too. You search for something, and then Quora takes that as an invitation to send you a bunch of spam. To make it worse, it seems impossible to control/prevent this through account settings. Opt-out doesn’t work. It got so bad I had to just completely block all email from quora.com. I still avoid clicking Quora links in search results because of this, even though I’ve blocked email from them. I guess it is a grudge. The bad thing is, I used to be active on Quora and enjoy its content, but something happened at some point a few years ago, where they became aggressively spammy.