Goodbyes are never easy but they are a part of life. Why do we write good bye letters? It is mainly to let the people you are interacting with know that you are leaving. It is also a time to recount the good times you spent with them and acknowledge their role in your life.
Goodbye letters must be warm and friendly without sounding sentimental or artificial. The tone should have genuine warmth. Keep the letters simple and short. You can briefly mention the reasons for your leaving.
While recounting happy days and times, it is also customary to thank the readers for their help/support/advice/guidance. Such acknowledgement always conveys warmth and gratitude.
Partings must always be on a positive note, so whatever be the reasons for your leaving do not let any negativity creep into the letters.
It is a good idea to leave your future contact details so that the reader/s can keep in touch with you.