Rule #1. Unless you know the person is openly trans and talks about it, you don't out them. Period.

I found out a certain writer I admire was trans when his name showed up on a list of female writers posted by some obnoxious TERF, and I was so mad. I don't need to know and I can't *unknow* it. (I can, however, correct anyone who mistakenly thinks said writer is a woman, which as he is Asian and writes under an Asian name, white people aren't always sure).

It was soooo obnoxious to do that to him. Like just...no...stop...