What is meant by Authorized Recipients?

To protect our customers from spam, we have restricted email sending under the Sandbox account to a list of authorized recipients only.
You can invite recipients and once they accept your invitation, you can start sending test emails right away, with no extra steps like adding a credit card or buying a custom domain, IP address etc.

The maximum number of allowed recipients per sandbox account is 20.

To manage your authorized recipients, go to your Settings and click on "Sandbox" tab. You will see a Authorized recipients dashboard there.