JIRA sends lots of email, at first I thought they were getting paid for every email they send but until now I haven't found any proof.
There's a couple of ways to lower the amount of emails you get from JIRA but I'll focus on two:
This is something you can manage yourself pretty easily. By default JIRA adds you as a watcher to all issues you update, transition, comment on, etc.
By becoming a watcher on an issue you most likely will get an email about every change! By disabling this auto-watcher in your profile preference you take full* control over which issues you watch (and what updates you get from JIRA)
* Full control will only be granted if the notification scheme of the project has been setup to only send emails to Watchers of an issue. See the next part of this blogpost: Update when an email is sent
As I mentioned in the first part, when and to who an email is send is completely configurable. JIRA uses a concept called Notification Schemes to do so. I won't go over the details on how to configure a Notification Scheme here but if you want to know more, checkout the very comprehensive documentation of Atlassian: Create a Notification Scheme or this great blogpost from TechSolCom.
In short: a notification scheme configures when (what action) and to who an email will be send. The Default Scheme will send an email for every event to the Reporter, Assignee & Watchers of an issue. I guess you now understand where the JIRA emails are coming from!
An interesting approach which I'm a big fan of is to limit the emails to be send to Watchers only! This allows all users to decide on an issue per issue basis whether or not they want to keep up to date.
Feel free to post them in the questions and I'll be happy to answer them!
If you want to see on which issues you already are a watcher you can use this JIRA Filter:
watcher = currentUser()
If you want to remove yourself as a watcher from all these issues you can use the Bulk Edit mode of JIRA (yes I've cut out some frames to make the gif shorter ):