Mail stops after 10 Seconds

Mail always stops 10 seconds after opening it with the comment: "Mail wurde unerwartet beendet. Klicken Sie auf "Erneut öffnen", um das Programm erneut zu öffnen..." I work with OS X 10.9.5. and I use Mail Version 7.3 (1878.6). The problem just arose today for the first time. Restarting the Macbook does not solve the problem.