I have several email addresses, some which haven't even been used yet and guess what some of them get spam.
It entirely depends on what the email address is as dictionary attacks are commonly used in the hope of hitting valid addresses. I have a couple of these type of addresses that weren't in the public arena, but they get spam
One of my ISPs I frequently find spam emails coming with whole blocks of email addresses for email addresses of that ISPs user. My suspicion was that their databases were hacked and the emails harvested otherwise how would an email address get into the public arena where it might get harvested.
So there is more to this than meets the eye, the email address I use on the forums, gets very little spam and that has been around for some time and used in multiple locations. Alwil software doesn't divulge emails to third parties, I have been an avast user for five and a half years and haven't come across anything to suspect otherwise.