I'm one of them. Those newsletters are spam. I would never sign up for a newsletter and somehow I'm getting those too. If my intent was not to get the newsletter, it's unsolicited mail by definition, i.e. spam.
Stop spamming me and I'll stop flagging you. Period.
How not to be flagged as spam:
- There should be a checkbox clearly visible and it shouldn't be pre-checked.
- Your "kind" product reminders are obnoxious too and I'll flag them as spam as well. Did I ask you to remind me of your product? Nope. Unsolicited then.
- If you ToS say I agree to receive mail, guess what? I don't agree, I just want to try your product. I'll flag you in a breeze.
- Social reminders like Twitter's trending around me or people I might know? SPAM! I don't care if I can disable these, I didn't enable them.
- You want to offer me discounts but I didn't ask for them? Flagged!
- I submitted a paper to a conference and it got published? Dozens of "calls for papers" in my inbox. Flagged, flagged, flagged, flagged!
- Calling it a newsletter or adding a tiny "unsubscribe" link won't hide the fact that it's still spam. I didn't click subscribe, I shouldn't have to unsubscribe.
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EDIT: Woah, this seems controversial. Lots of up- and down-votes.
Dear product owners, downvoting me here won't change the fact that me (and your fellow users) will still flag the shit out of your unsolicited mail. I guess it pays if you keep doing it, but you should direct your energy far from that downvote button and closer to "ways not to annoy my users".