Even if you don't organize meetings and send invitations in Office 365, you may get invited to meetings now and then, so it's a good idea to know how to respond to a meeting request if you get one.
When you've been invited to a meeting, you get a special e-mail message that offers these buttons:
Accept: Outlook on the web automatically adds the meeting to your schedule and creates a new e-mail message to the person who organized the meeting, telling that person your decision.
Tentative: The meeting's automatically added to your schedule. A new e-mail message goes to the person who organized the meeting.
Decline: Just can't make it? If you click Decline, Outlook sends a message to the meeting organizer to convey the bad news. It's good form to add a business reason to explain why you're missing a meeting -- "Sorry, I have a deadline," rather than "I have to wash my aardvark" or "Sorry, I plan to be sane that day."
Propose New Time: If the meeting organizer chose an inconvenient time, you can suggest another by clicking Propose New Time.
Important: If you do not send your response back to the organizer, they will not be able to track your response. In other words, it will appear as though you have not responded even though you had accepted or declined the meeting request.
Note: If you cannot remember if you have responded to a meeting request, open the meeting from within your calendar and your response will be listed just below the title of the event.