The written abuse has included threats of physical violence and he has fears for the safety of his family.
Speaking ahead of tomorrow's home game against champions Reading, Blackwell said in the Yorkshire Post: "If people are not happy with what I am doing, I don't have to hang around here. If they don't want me, then that's the way it is going to be.
"When I get threats to my well-being, you have to wonder why people do the job sometimes. Why it is happening now, I don't know. Frustration has a terrible way of manifesting itself, but don't people think we are frustrated too?"
But Blackwell is not planning to involve the police at this stage. "I have spoken to people at the club and they feel we should leave it at that but clearly I am going to watch what I am doing because I don't know what might be around the corner," he added.