I have been under cyberstalking. But it is very difficult to prove the source rigorously given that the sender can fake the header information. Is it possible to report the stalking to the police?
You can report cyberstalking to police, but it is unlikely that they will do anything about it if they can't prove who did it easily in a definitive way without advanced IT resources. At a minimum, a police report will document with a third party that the problem existed in the event that the situation escalates later.
Most police departments are not equipped to do sophisticated investigations of Internet based crimes, and in general, police departments tend to put a low priority on crimes that don't involve physical harm or damage to property in the thousands of dollars. Even if the case is presented to them wrapped up in a bow and basically solved with solid proof in hand, it is hard to get their attention.
The FBI is better equipped to deal with cyber crime but also has higher thresholds of harm before they are willing to use their scarce resources to pursue a case.