I am a fresh graduate and after a long search I have been fortunate enough to get two job offers. Both jobs will start in three months. I have decided which one to take but I am not quite sure when and how to decline the other one. I know I should let them know as soon as possible that I won’t be joining, but it could be my back up in case anything happens with the other job during this period of time. When is the best time to do it?

Also, I plan to turn down the offer by email, thanking them for the opportunity and letting them know how much I value the offer but have decided not to join. Would that be appropriate? I want to make sure it doesn’t close doors for future opportunities. What should I say and should I give the real reason why I decline the offer?