I need to tell someone anonymously their H is unfaithful

[Popeyethenailor]

I need to anonymously tell the wife of an abusive and chronically unfaithful man that he is unfaithful to her.

I presume she knows about the abuse, as it happens to her, but from conversations with her I feel that confirmation of the infidelity will be the thing that will set her free and finally give her a reason to leave.

I have no vested interest in her knowing (I am not the OW,) I am actually related to her H, so see first hand what goes on and am privy to family discussions about it all. The rest of the family protects him and tells him just to divorce her when their DC are over and I find that very unfair.

If it was revealed that it was me who told her then my family would shun me and consider me completely disloyal.

Which comes to your advice. How do I do it in the most anonymous way possible? A way where even if she showed her H and he employed a whole technology investigations team to trace the message it wouldn't get back to me?

Not wanting to judge you here but let me tell you story. I have a friend whose ex did this. He was abusive and so was his family. The wife was utterly hopeless in terms of grit and we used to pity her for it but could not think of a way to help her. Then he cheated. For over a year. We did not know but she found out after that year and then quit. I raised hell once I found out because she was close to me. I did not give a rat's sh** for what anyone thought of me or whether I was welcome in that side of my family anymore. Me and my family are better off without such bastards and I am still helping her emotionally though I can't help financially.
In your case I think some kind of financial issues are involved I suspect. Or may be some really dear one(s) is at stake. Either way, i think you are going to keep a regret for the rest of your life if you don't help her whichever way you can. Pls don't tell me you are not obliged to. Others worked for the rights women have today.