Let him know how delighted you are, and reassure him that he made the correct decision. Tell him what a difference his gift is going to make. If possible, include a Welcome Kit that provides additional information about your organization and why it deserves his continued support.
When you launch your next campaign, help him graduate from being a new donor to being an active donor. In the first paragraph of your letter, address him as a new donor so he knows you’re aware of his status. Then reinforce that fact, before making your ask, by stating the date and amount of his first donation. But if you’re tempted to ask for an increase in the size of his next donation, remind yourself that your objective isn’t to raise as much money as possible from him during one year; it’s to build the relationship for the long term.