To Thank a colleague via email, you will want to email that person directly and cc post@rypple.com, so the process would be

To: colleague@company.com 
CC: post@rypple.com 
Subject: (can be anything you like)
Body: include the hashtag #badge (this hashtag must be an existing badge in your Rypple)

Post@Rypple.com in the CC: field ensures the content goes to your company feed and everyone can view what you've posted.