Keep your chin up. You haven't lost it till you've lost it. Most people are nervous during interviews, she knows that. How was the content of your answers? Did you share what you wanted and answer the questions fully? If you did that, why wouldn't you get the job? Are you fit enough to be a mail carrier? Can you walk far distances or drive the mail car? Are you prompt? You're stutter shouldn't stop you. Even if you get discouraged, keep a positive mind set. If you don't get this job, think about what factors you can control and learn for your next interview.