Donation acknowledgment letters are more than just a donor tax receipt. There are certain items to include for tax purposes.What do you need to include in your donation acknowledgment letter? What is required in a donation acknowledgement letter? The certificate of acknowledgment (PDF) must be in the form set forth in California Civil Code section 1189. A donation acknowledgment letter (sometimes called a donation receipt or thankyou letter) is an email or paper that recognizes a charitable contribution.