I have used this for many years. Essentially, you create an email address, which you then use publicly e.g. when signing up for freebies. It allows you to protect your real email address from potential spam. It also allows you to forward any email to your real account.
Any email that is forwarded is preceded with [despammed], so it's real obvious where it has come from.
The filteration is really good, and stops most (if not all) rubbish getting through - if in any doubt that signing up to a freebie may result in spam, then sign-up using your despammed address.
I'm sure that there are other services like this, but this is the one I have been using, and works well for me. Hope it benefits some of you guys.