As a new member of the community, I run into same issue than writer of this post. Basically that by default, all the categories are set to Watched, which results every new post being sent instantly via email. I think this is fairly intrusive, and I don’t remember ever witnessing it on any other forum I have signed into. I think it would be good to reconsider this practise.
For those who want to remove categories being watched, it can be done from Profile > Preferences > Tracking > Categories : Watched
I signed up this week and this setting drove me mad! Like you say, I don’t think other Discourse implementation have this by default. It was a relief to turn it off and now I can concentrate on the topics that really interest me.