The letter must explain who is gifting the money, where the donor's funds are coming from and the relationship between the donor and the recipient. A gift letter for a mortgage verifies the source of a homebuyer's gifted down payment funds.A gift letter is proof to the lender that the funds were gifted to a homebuyer for their home purchase, and not a loan or borrowed money. A down payment can be hard to come by. One option is to be gifted the money, but this has certain requirements, such as a gift letter. To use gift funds, you must provide a gift letter proving the money is not a loan.