This is why I always type in fake information if I'm dealing with a website that I know doesn't need my info. The only reason a website would ask for my email address when I know they don't need it is for selling it or spamming me with it later. So think about whether or not you actually want the business you're giving your information to to be able to contact you. If not, make up something else. They don't need to know your gender, age, etc., and they have no right to require it. Sometimes I go and set up a quick fake email to use for their verification email and then I never use that email address again. Even with all of this, I have ended up on some crappy spamming lists - behold, this website.
Always be suspicious when someone is asking for any information from you. I know we all want to make contacts, but if there's no good reason why someone would actually need that information in future, then don't give it to them. Once your email is on one of these lists, it's there forever. And the list just keeps getting resold and circulated, so new scammers are just going to keep coming in to your inbox.
The junk I post on this site actually goes into my junk-mail folder (I dig it out and post it for you) because I have my email set to only allow mail from people I know to get into my inbox. This is also an emergency setting I was originally reluctant to implement. But it has been in effect for about ten years and is working very nicely. If you're being bothered by junk-mail you could try this setting. Most email providers have it.
A good way to test if someone is selling your information is, when registering or giving them your information, give them the right email but a totally fictitious name, something you'll remember. That way when you receive offensive spam addressed to Mr. FakeName you know who sold your information. Problem is you have to make up a fake name unique for each request for information and remember which one went to which.