When you have a complaint, writing an email is okay. You need to provide a clear picture of for the reader because there is a tremendous amount of room for misinterpretation and misunderstanding. If you need to write a complaint think of the following:
Select all that apply.
If you think a mistake has been made, clarify why with the person as to what you think the error is.
Explain how you made attempts to solve the problem yourself.
Offer suggestions as to how to fix the problem.
Explain why it is important for the person to resolve the problem.
Type in all caps as it helps your meaning.
Briefly state the history of the problem.
It is okay to disagree with someone without being disagreeable.