Any one of the following will prevent email notifications from being sent:

You have added a Delegate and selected ‘Send meeting requests and responses only to my delegates, not to me’. (e.g., Tools | Options | Delegate).
You have your calendar set to auto-accept meeting requests.
You set ‘Author’ permissions on your calendar. This allows a person to open your calendar by choosing ‘Open a Shared Calendar’ and schedule a meeting directly on your calendar. Therefore, no email notification is sent.


Check the e-mail sort you may have set, that can end up putting all the calender notifications at the bottom of all your e-mails.