Sending a thank you letter to people who contributed to your organization or cause is good etiquette.
On behalf of all of the staff and volunteers who make up the body of [Organization name], I would just like to say "thank you" for your generous support in the form of your tax-deductible gift of [Donated amount] on [Date].
The work we are able to conduct on a daily basis would not be possible if not for the help of such compassionate donors like yourself. It is because of people like you that we are able to continue to advance our program's mission with each passing year.
Your donation has helped [Organization name] toward building a better and brighter future for the individuals we work with on a daily basis. We could never have made it this far without you, and in future editions of our monthly newsletter, we look forward to sharing more with you about the opportunities and successes we work to actively build in people's lives. We are very excited to watch the months unfold before us as we come closer to accomplishing our mission.
Thank you so much for being a part of this organization and for supporting such a critical cause. The smiles we are able to bring to people's faces on a daily basis are only made possible through generosity from people like you. If you have any questions about our organization, you can reach me by phone at 555-555-5555