Unsubscribe is one option. This must be one of many cultural differences but here up Northern Europe, but this seems to be quite common way in Europe, at continental anyway, unsubscribe-links are rarely used. It’s easier mark emails as spam.
I blaim companies, but lets not take that road now 
I asked from my users and actually no one (in the meaning: who answered, of course) wanted emails just because of topic activity.
I dig a bit logs and accounts. It looks like when an user falls among digestive email receivers that user is a lost case and never come back. That can, and do I believe, mean I have annoyed people with too many emails and after some time they just marked my forum as a spam.
I can be very wrong and just doing hasty conclusions… but I don’t think so. I kind of know my audience and on general level how SoMe-background people have tendecy to act.
If someone now ask why the heck I didn’t adjust settings of my forum, because that’s why those are there, and I just used defaults (sorry guys, defaults are for american tech-savvy users; I know why it so and I’m not whining
), is askind very good question indeed. Perhaps I’m lazy. Or just dumb.
Shutting down emails totally is quite bad idea. It can be done of course and I tried it very short time. And I got a reminder very fast. One user wanted sign up, couldn’t do it and because she was one of my (really, is there some synonyms to use because I really dislike my) active ones from Facebook group she sended PM there. She did not wanted use SSOs like Google, Microsoft and Facebook because she didn’t trust on those — and that is really common way to think here and that’s why SSO is not always the best option.
So I turned emails on again and returned plain username/password login.
And at this point I did what I should do at first point and what I’m whining about all the time: let users make decision. Yes, I’m quite stupid every now and then.
So I turned off all email notification settings as widely I could. And next I have to take totally different approaching to task how do we educate an user.
I tried to teach them use settings where they can reduce amount of emails. That was bad direction. I basically said to users that I’ll annoy you purposely and if you don’t like it you have to act. BTW — that is the reason why emails must be opt-in here in Europe, not opt-out as in so many cases in USA.
Now I do totally opposite thing. I tell them if you are motivated enough and really want these emails you have to this (but I remaind you couple times that we are here’).
So — my topic is totally wrong .Something like that is really common when there is an issue one can’t solve out and still trying to figure out something. Next thing is asking how do I do this trick instead of I have this issue, do you have any ideas.
But… one reason to start this topic wasn’t actually my needs. Sure, I had some headache attacks because of amount of emails, but I had some feelings the linked topic started without thinking why, but moved rightaway to how. As really many topics here.
I should ask at #community how do you guys live with spam fear or do just have enough users, returning and new ones, and you just don’t need to care — or is your audience such target grous they are still using email and they can live with excessive amount of electronic mail 
(All typos and grammatical errors are mine and mine only)