I may be old fashioned, but I still mail out a handwritten thank you card to anyone that does something kind for me, brightens my day, or gives me a gift. As an organization that receives grant funding, it is extremely important that you thank your funders when they donate to your cause. Creating relationships with these funders will help you to secure additional funding in the future. Not to mention that they truly do deserve your gratitude. However you choose to thank your funders, I suggest that you do so within 30 days of the receipt of your funding.