“I’ve reviewed this message” checkbox

Step by step

1. Go to Communications and finish composing your message.
2. Check the recipient count shown just above the checkbox to confirm how many people you’re about to reach.
3. Check I’ve reviewed this message.
4. This unlocks Send now, which stays disabled until this box is checked.
5. Click Send now (see below) once you’re actually ready to send.

This is a deliberate speed bump so a campaign to your whole list can’t go out from an accidental click.