If groups allow people to request to join, their membership request needs to be approved by a group administrator, group moderator, or an organization owner.
If all or some messages in groups need to be reviewed (moderated) before they are sent to the group, they need to be approved by a group administrator, group moderator or organization owner. Some information on why the message is held or discarded is shown in the review panel when you click on the message.
Messages awaiting approval appear in the For Review dashboard.
To see old messages that were rejected (because of the security settings excluding certain users, or because they failed moderation), use the Show rejected messages checkbox.