My divorce was August 4, 2011 in Colorado. He has to pay spousal support but with every check, I get a nasty letter saying I am a thief, I have taken things which were not mine, etc. It's getting really upsetting, especially when he is threatening to take me back to court. I do not respond to his letters as I will not get into a "fight" as I want to go ahead with my life. What can I do to stop this harassment?

Ignore him. The fun (for him) will stop when he gets no response.
I'd cash the check with a big smile on my face and totally ignore him.

In the meantime save the letters in the event he escalates his behavior.

I agree wholeheartedly with Judy. Cash the check and don't respond to him. My mother always said to me about my little brother, "Ignore him so he doesn't get any satisfaction from you."

And yes, save his letters.

Yes, stop even reading the notes, just take the check and cash it.