I don't spam
I hate spam, I have 4 email accounts and I get way too much of it. I don't need my private member enlarged and don't feel like making $10 million helping a Nigerian con artist find long lost relatives.
So about a week ago, a prospective buyer registered for listing alerts for properties that met his criteria and I replied with a thank you and set him up. He looked at the first day's notifications and then didn't open any for the next week.
Today, I received an email from him: LEVE ME ALONE OR ILL CALL THE COPS!
Sure thing buddy, the listing alerts have been deleted and so have you.
I'm amused because every listing alert comes with an automatic opt out and every email that I send will always be FTC can spam compliant because I hate spam as much as you do.
A "transactional or relationship message" – email that facilitates an agreed-upon transaction or updates a customer in an existing business relationship – may not contain false or misleading routing information, but otherwise is exempt from most provisions of the CAN-SPAM Act.
Obviously, he must have forgotten that he requested to have listing alerts sent to him just a week ago before threatening to call the cops.
But can he spell leave or will he just make me ill. 
By the way, while I'm on the subject, if you register with a bad email address, you can't receive auto notifications and you can't receive your password to log in for advanced search.