In the introduction:
- you say who you are: give basic information about yourself and your relationship to the person you're addressing. You do not need to state your name, as that will be evident at the end of the letter.
- you state the reason(s) why you are writing the letter.
In the main body:
- you give details about the problems you encountered and wish to point out.
In the conclusion:
- you should mention what you expect the person you are writing to, to do about the problem. The conclusion is therefore a call to action.
- you should also remind the recipient of the letter of your feelings (disappointment, etc.)