Endorsement letters should include the sender's personal information and position, who or what is being endorsed and the sender's relationship to this person or project. It should also include several pieces of evidence supporting the endorsement, the sender's contact information and a short summary reiterating the endorsement.
The sender should open the endorsement letter with his or her full name, position and contact information. He should include any expertise he holds that would lend credibility to the endorsement. If the letter endorses a person, the sender should also make note of his relationship to them, including the history and duration of the relationship.
Evidence should be included that supports the endorsement in an effective and positive way. The writer should choose specific evidence that is pertinent to the endorsement and support it with personal anecdotes or experiences. For example, when endorsing a person, the sender could support evidence about her being a strong worker by explaining a situation where she went above and beyond to finish a project. For an effective letter of endorsement, the sender should include as many relevant accomplishments and abilities as possible.
The sender should end the letter of endorsement by summarizing his points and reiterating why his endorsement should be important to the reader. The sender should also offer to follow up with the receiver of the letter should there be any questions about the endorsement.