Many spammers simply guess at email addresses. e.g. if they send spam to
[email protected],
[email protected],
[email protected], etc, there's a good chance that at least some of the messages will be delivered.
However what the spammers would really like is to have a list of email addresses which they know to be genuine. So the last thing that you would want to do is to add your own address to such a list. But that's what clicking 'Unsubscribe' (or similar) on a spam email actually does! i.e. it effectively sends back a message saying "Yes, I'm real. Please send me thousands and thousands more spam emails!"
Never, ever click 'Unsubscribe' on a spam email! It's just asking for trouble!!!