The hold queue for emails from senders Hemma doesn't recognise yet. New email lands here instead of going straight into your project.
You see the message preview, decide to approve or reject the sender, and that decision applies from now on — both retroactively (held messages are released or quarantined) and going forward.
The waiting room exists so contractors who don't even know your project email yet can email you without their first message disappearing into the noise. Approve once, future messages flow through automatically.