The Reporting - Reminder - Send - Preview button can be use to preview reminders prior to send.
To help users test email reminders, this should default the From address to the same email contact as would be used when the reminder is actually sent i.e.:

• the REMINDER email contact associated with the customer's practice location, or

• the REMINDER email contact associated with the default reminder practice location, if the customer doesn't have one; or

• the REMINDER email contact associated with the practice; or

• the preferred practice email contact