When you receive a message, task request, or calendar invitation, you are able to respond with a meeting request. The meeting request invites everyone, tagged in the original message's recipients list, as Required Attendees. Additional recipients located in the Cc line, by default, as Optional Attendees.

1. Open the message you wish to respond to. From within the Respond group click the Meeting Button.

2. Complete the response by adding in the Location, Start/End times, add or remove attendees, attachment or use the Scheduling Assistant to find the best meeting times. 

3. Click on the Send button when finished