Endorsement is a support, authorization, approval of something, while writing a letter of endorsement you have to show advocating to a person, an idea, a movement, or an organization. You should introduce different types of information with different aspects, to make sure what kind of effects the endorsement is going to leave. Your stance should be very clear about what you endorsing. In an endorsement letter you should stand out clearly that you are giving your consent, or you are supporting something, you should introduce yourself and your endorsement clearly. You can also mention your position or title or any expertise that you hold, which can aid your endorsement in any way.
You should state the reasons for the endorsement, which can take you into a better position to impact the endorsement you have made. If you are endorsing a person for a title for a title or a job, you should include the history of your relationship in a way that validates your endorsement and proves it a right choice. It is also good to mention that for what purpose this endorsement should be used. It will leave a good impact of your endorsement, if you will bring up or point put the qualities or the reimbursement of something you are endorsing.
Your endorsement should also have a brief detail about you, your information. As endorsement could be of different types, so every type should be having a different kind of endorsement. You should repeat your endorsement at the end of the letter, summarize your main points that why and what kind of effect your endorsement has and why it matters or what importance it has. Let it open for any further information or for any kind of quarries. For the convenience of the readers, sample of endorsement letter is also attached with this template.