The comings and goings of meeting requests and their related calendar entries are tracked in Outlook by something nick-named the "sniffer."
You'll see the work of the sniffer by looking at the Infobar of a meeting request in your Inbox or a meeting entry in your Calendar.
Note Requests and responses need to linger in the Inbox for a short period of time so that the sniffer has time to notice them and can add them to your Calendar. The exact amount of time required will vary, but it can range anywhere from 30 seconds to five minutes, depending on your specific setup and what else Outlook is doing when the meeting arrives in your Inbox. If you're in a hurry, you can click a meeting-related item in the Inbox and the sniffer will be alerted to it right away.
When you're a meeting organizer The meeting requests you send to your attendees, as well as their responses, are detected by the sniffer as they sit in your Inbox. The sniffer then updates the Calendar and the requests themselves with the relevant information. For example, you can look in the Infobar to see the responses that the sniffer has counted in your Inbox.
When you're an attendee When you receive a meeting request, the sniffer automatically enters that request as a tentative item in your calendar to help reduce your chances of getting double-booked. Need help keeping track of whether a meeting has been rescheduled? The sniffer can help there too. For example, if the sniffer has detected a later version of a meeting request, the Infobar of that request may say "This request is out-of-date."