How to sing out of communities emails?

If you check the link below, you should see the 2 forum categories you are following. If you click the lPad category, you should see “Following” in the top right of the page. From there, click “Following” to stop subscriptions to that forum category.

https://discussions.apple.com/profile/ilivitup/subscriptions?page=1&content=filterCommunities

In addition to stedman1's excellent suggestion, email prefs are also controllable from your main profile page:

ilivitup’s Profile - Apple Community

where you will find an "Edit Profile" link in the upper right:

When the Edit page is open, scroll done to find this section:

Checked as shown above, you will not get flooded by mails due to others' posting, but will be notified of having points awarded and other nice things like leveling up.

The advantage I find is this method is universal across categories. You do not have to set prefs for each forum section you visit, yet you will still get the occasional useful notification from Moderations about your status here.