In general, Sifter is very judicious about sending email notifications to help keep the signal to noise ratio under control. Sifter will generally only send you a notification if you're directly involved in an issue or if someone mentions you in the comments for an issue.
If you go to Settings and click the Notifications tab, you'll see all your options for email notifications there. Selecting all of these won't mean you get notified of every single issue no matter what, but it will enable you to make sure you don't miss out on activity related to issues you follow or to which you are assigned.
You can also connect your Sifter account to Zapier in order to route notifications of any new issues to email and other places. For instance, we push notifications to our team Slack account any time someone creates a new issue. This way, everyone keeps abreast of the activity without cluttering their email inbox.
You can send notifications to team email lists, chat rooms, or even SMS. You can also use Zapier's filters to send notifications for specific types of issues. For instance, you may want to receive an SMS if there are ever any new issues in the "Security" category for your project.