I'll send a letter to you. (OK) I'll send you a letter. (OK)
I'll send you to that place. (Correct. It has a different meaning than the first two. It means: I will direct you to go to that place. eg. Johnny hit his little sister with a toy and she cried. His mother sent him to his room.) I'll send you that place. (No, unless "that place" can be put in a box.)