Tree problem with neighbor

Our neighbor has expressed concern about our large spruce tree. The tree is about 50' tall, is entirely on our property but is sitting between our house and his house. He is saying that the tree is "leaning" towards his house and that he is concerned that it will fall on his house. We brought in an arborist who told us that the tree seems healthy and is not leaning toward his house, but that it is slightly growing in that direction because of the position of the sun. We let the neighbor ask questions when the tree expert was here and the tree expert reassured him that the tree does not pose any more of a risk than any other tree in the neighborhood and that although there is no guarantee that any tree will not fall, there is no reason to believe that this tree poses any significant danger to him. The neighbor apparently was not satisfied with that opinion and has pursued the issue by having a lawyer send us a certified mail. The lawyer has expressed her opinion that the tree could fall during a storm or heavy snow and ice and asks that we "as a good neighbor" should take action and resolve this matter so as not to cause any friction with our neighbor. Should we answer the certified mail and address the issue? Should we get an arborist's opinion in writing? Should we take pictures of the tree? How can we protect ourselves from a future law suit if in case the tree ever does fall and what are our rights? Must we remove our tree or prune it because the neighbor has requested that? The tree seems like a beautiful healthy blue spruce and we really do not want to kill a perfectly healthy tree but we are concerned about liability. Please advise us on the best course of action. Our property is in New York.

Thank you

Get the opinion in writing but if it is a healthy tree and poses no imminent risk, you normally are protected and his insurance needs to cover acts of God or other freak storms etc.