Whenever you create a new to-do based on an email, Wunderlist for Outlook will save as much information as possible to provide a string connection between Outlook and Wunderlist.
1. The Mail Icon
Mails that you have used to create a to-do will get a small Wunderlist icon so you can directly see you have already worked with that email.
2. Open the task
On these emails you can directly open associated tasks from the ribbon menu at the top.
3. Tracked across conversations
You can even find corresponding tasks for mails that are in the same conversation. So if you reply back and forth, you'll still be able to open corresponding tasks (while you'll not see a Wunderlist icon on the mail)