>Do Twitter employees have a safe place to discuss this?
How did people communicate before the invention of Twitter and employer provided email and slack channels?
Bulletin board systems?
Phone, email, and in person are safe if you trust your counterparty?
Personal email, obviously. Never discuss anything of this nature on any communication medium that is owned by your employer. There's a reason "Direct Message" labeling overtook "Private Message" in chat apps.
Depending upon how sensitive I’d generally try to avoid written communications in general. It’s easy for even well-meaning friends, current or ex-workers to forward something without thinking it through.
On them. I absolutely would have no trouble finding / creating a space and the Twitter people are likely far more capable.