@Zelduh Yes, it is unethical and illegal
The fact you are thinking of this, and you still have the law partner speaks volumes
I know it is a crime (both a Federal & a State felony.) Gmail has a thing where you can grab it back, but my law partner does not use gmail.
Years ago, like in the 1990s, one of my geek clients was working on an app to help ppl retrieve an errant email someone sent to the wrong address.
My client is absolutely LIVID. Nothing I can do at this point.
I've practiced law for almost 40 years. I think I will lose this client.