You can unsubscribe from our Spiceworks email on your profile page, and here is an official unsubscribe page for our company: https://pages.swzd.com/swzd-subscription-preferences-page.html
However, it isn't us sending you the spam in most cases. It is the individual companies that sponsor the event and give things away. Their offerings are useful for some, of course, but if they are not to you, then you'll have to be proactive about asking to be added to their do not contact list or removed from their contact list, whichever way they do it. They're required to allow you to opt out. And if the same person contacts you twice and you've already said no, then an email filter can be useful.
I'm absolutely not saying that I am fan of spam... I'm definitely not, especially the ones that I get that automatically open tickets in our helpdesk, but as long as the vendors are following the rules, you should be able to unsubscribe.