A good apology letter includes the apology, an acknowledgement of the specific wrongdoing, an understanding of the impact of the mistake, an explanation of how the mistake was or will be corrected, and an invitation for further discussion if desired. The letter should end with a reiteration of the apology.
An apology letter must be sincere and succinct and sent as soon as possible. Delay or evasiveness reduces an apology's effectiveness. Excuses and rationalizations are best avoided because the writer may seem to be shifting the blame away from himself. Clearly stating the mistake and its resulting harm shows the recipient that the apologizer understands what he did wrong.
A professional or business mistake warrants a formal tone and approach, typed in a standard business letter format. Apologies to a personal friend or family member can be informally written, perhaps even handwritten. Whether professional or personal, an apology letter still contains all the elements of a complete apology: regret, responsibility and correction. In some cases, an offer of restitution is appropriate.
An apology letter is a step toward reconciliation. The apology is an opportunity to acknowledge one's humanity and demonstrate personal integrity. A heartfelt, well-written letter has the potential to mend and restore a relationship.
Apologyletters.net and Perfectapology.com offer a variety of apology letter samples.