I think you may need to be more specific. Are you creating an email in TB and then choosing the "attach" option? Or using a "send by email" right click or something similar ( you haven't said what OS you are using so I'm assuming a version of Windows since you seem to have Outlook)? Is TB your default email app in Windows ( assuming that it is Windows)? Or is Outlook. If you right click an item to send it in an email the OS will choose your default email programme. If that's Outlook it will try to send it using Outlook.