Unsubscribe? Is that such a hard concept to grasp?

We just got 2 calls in 2 days from our ISP about spam messages.
We do send out a monthly programming email, that complies to the CANSPAM act, including a working unsubscribe feature. Is it so hard to unsubscribe instead of clicking spam, if you're getting our email you gave us your email address when you signed up for your library card.
And little to my surprise AOL is the one causing the biggest issue.
OIY.
I don't feel like setting up our own email server in house, but I may have to now, yay Ubuntu.