My bf's friend trying to break us up?

My boyfriend and I have been dating for almost three years. He is 28 and I am 22. We're generally happy in our relationship and like to think we might marry a few years into the future. There is a girl he used to be friends with, long before he even met me, and as soon as we began dating, she has tried to steel him away. Well, as soon as she tried, my boyfriend immediately broke contact with her and he was quite unhappy that he had to loose a friend. However, when he ended their friendship over her actions (she was having people spying on him, calling him, etc) she and another of her friends have been sending me harrasing anonymous emails. These people are not in our life (the girl herself is not even in the same country anymore) yet herself and her friend continously send me these messages through myspace, email, etc. I want it to end but I have no proof that it is them. What should I do? They still find outlets to contact me even if I change my email and myspace. I find it absurd that after so many years, she is till this persistent.