For example, if someone emails me about my product, is it ok to add them to a mailing list for product updates?
Thanks.
Story time: I asked a Logic Audio plugin developer a question about one of their plugins that I might have been interested in using. They put me on their mailing list without my requesting it, and over time I was getting tens of emails a month from them about that product and others that they had. I was ignoring all of them since they were literal spam about things I simply wasn't interested in.
They got bought out by another company that sold Music e-magazines as well as software, and suddenly I was inundated by spam from all their different areas.
It took me quite a while to get off their lists, and I assured them that because of what they had done, I would never buy anything from them, no matter how incredible or desirable - they'll always have competition, and I'll be going there instead. All because they mishandled my one question about one product of theirs that I didn't even own (and henceforth never will.)