Fienta has a tool for sending complimentary tickets to your volunteers, sponsors or winners of social media campaigns.
You will find it from "Orders" or "Orders and attendees" menu item in event context:
The tool allows you to select a set of tickets and send it to one or multiple recipients. If you enter a list of email addresses, each will get a unique set of tickets. You can add personal message to the emails and choose whether to display normal prices or "Invitation" instead. If your event is listed in multiple languages, you can select the language for generated tickets and email.