Human beings are all about mistakes, anyone can make a mistake at any point and usually mistakes are made unintentionally. A letter of mistake could be in two ways, either it could be when you have made a mistake or you are accepting it, or someone else has committed a mistake and you are the aggrieved party.
In the first instance if you have made a mistake it is wise to accept your mistake as soon as you come to know that something wrong has happened. It will help you to prove that you are innocent and the mistake was unintentional. You should accept that something went wrong or was not as it was expected, therefore; you promise for compensation. This compensation could be in any way but do not make such promise unless you are sure that you are going to do it. You should apologize for the mistake in a decent manner.
If some one else has made a mistake and you are the aggrieved party then you should write as early as possible pointing out that you have not reached a product or the service given were not up to the mark of satisfaction. In both the cases your letter should communicate clearly, you should explain whole scenario but keep it friendly, the letter should be concise but comprehensive. The tone of the letter should be respectful and you should not blame anyone for the wrong done, it leaves a bad impact, instead try to take things to a point of settlement and mutual consent. In both types of letter of mistake it is good to assure the other party that you believe in them and want to keep a good business relation in future. End your letter reassuring that you trust the other party. Letter should address the recipient and should have a date on it and must be signed by the sender. A sample of letter mistake attached with this template will help you to draft your own letter of mistake.