Offer a polite, appreciative response that helps clarify what is expected of you.
Be sure you have a clear definition of your role from the outset to avoid problems later.
Repeat the details of the agreement so your reader can respond to any misunderstandings that may have arisen.
Clarify or amend the terms of your agreement, if necessary.
Be accurate. Check (and double check!) your facts before sending the letter.
Choose your tone carefully.
Confirmation letters should generally be brief and businesslike, but because they are the result of previous contact, you may wish to write in a more personal tone.
Send the letter within a few days of receiving the original letter, report, order, or other document.
Notify all those involved after receiving the letter of confirmation so that everyone is up to date on current happenings.
Be enthusiastic when writing this letter if you are the one who is being interviewed, considered as a guest at a workshop, given the opportunity to speak at a conference or banquet, given the charge to head a fundraiser, etc.
A well-worded confirmation letters helps you ratify, approve, strengthen one's resolve, or give new assurance of the validity of something.