I only mark the email as spam because I am ASSURED that my email won’t go onto any marketing lists. I only give out those addresses when I get such assurances. Thus, they lied to me when I signed up. I feel no guilt whatsoever. I would vastly prefer to only give out my snail mail address. The companies don’t need my email for a buyer’s reward program…a snail mail address would work just fine, if they didn’t want to sneakily spam me. If they’re going to use my email as a way to send me countless unwanted emails, then they should be up front about it, and let me choose whether or not I want to delete several emails a week from them.
I have a different email address that I give out when I WANT to receive email from a company. I can’t remember exactly which companies I’ve given that address to, but one of them will let me know when an author has a new book out, and ONLY sends me an email when a new book is coming out. This is information that has value to me.