If you have a Communications message in a draft or a scheduled status, you can delete the message entirely up until it's actually sent. Sent messages can be reviewed for statistics but cannot be deleted.
To delete a pending message,
1. Go to the Communications view from the navigation bar.
2. Under Pending Messages, locate the message you'd like to delete.
3. Click the trash icon to the far right of the row under Actions. A deletion cannot be undone so be sure this is the message you want to remove.