Hi, I don't know if it helps, but my xh could have written that email!
I have no idea where their brain is hiding. Many of my xh's accusations were totally untrue and based on things he had imagined I had said.
I don't know what your stbx was like pre MLC but mine was a sweetheart, and would never have written a message like that to anyone, let alone to the woman he had shared over 30 years of marriage with.
Now we are divorced he is less mean, but stil cannot handle any argument.