How do I automatically say Thank You? (Dasher)

You can automatically say 'Thank You', or anything else that is appropriate, after each game you play. It can be toggled on and off and edited.

Menu above: Edit > Settings > Playing 2 Tab > Under 'Postgame Actions'  you will find 'Auto-thank opponent'.
  
Checking the box causes an automatic 'say' to be sent to your opponent after the end of a game. This is most commonly used to say things like 'good game' or 'thank you'.   (The default is set to 'unchecked' and 'thank you')