Bandersnatch, Yeah I know what you mean, I'm sure that thought has come across my mind before when entering details in to less pro looking sites,
Worth mentioning, it may help someone, I do tend to get the odd email (although I don't remember the last) which is less advertising and an actual scam or imitation of a real website. If I'm ever unsure I open the message source (all emails come with this data attached and it can always be viewed easily, just find the button) this is around a page or so of gobbled script and hidden in there are the true source and IP of the email (even if just a temp or fake), as often they mask the source with a genuine email address so when you hit reply, it shows the real website email (or something close). When you find the actual source it will be something random like as5nkd@cd.dn
The quickest way to find it is to hit Ctrl+F while viewing the source (same on any browser I think) and type just @ and have a sift thought, you'll see your own in there, the "mask" and the source, which is the one you should be scrutinising.
I may very well be notifying some of them that I'm active, however this doesn't really work these days. What happens when an email address is sent to a non existent address is that the provider, say Gmail, responds by returning a delivery failure notification. thus the sender knows its not a real email address anyway (but he doesnt know if its active)- he's one up. but not for long, as these random email generators (a bit like random phone number dialling) generate HUGE amounts of emails – Hundreds of thousands a minute, but before a minute is even up, "Gmail" has already clocked whats going on, and banned it at the source, there are more things the wrong uns can do to dodge or change their address but due to glaringly obvious way in which they are working, it's impossible for them to out pace the providers by much – no doubt they share this security info with each other too. Further to that, there is also minimum time between accepted requests from unknown sources, usually 1 second – so they couldn't possibly send out 100k in a minute, even if they could generate it, unless they hacked someone else line, and if they're good enough to be doing these things, then they're going to have much bigger fish to fry………….
Hopefully a few tips can be gleaned from my ramblings there, I don't expect them to be valid for more than a few years, its something that constantly changes.