What do you need to include in your donation acknowledgment letter? We will mail you a gift receipt acknowledgement letter within 2 business days after receiving your gift.A donation acknowledgment letter (sometimes called a donation receipt or thankyou letter) is an email or paper that recognizes a charitable contribution. Please retain this letter as our acknowledgement of your donation. When acknowledging these donations, include the name of the donor, the number of shares, the name of the security, and the date when the transfer was completed.