My preview sandbox users used to have the email address "firstname.lastname@example.org" now, all user's show their live production email address.
Using the actual user's real email address allows the Preview environment to use the "Forgot Password" link during login.
Preview user objects have a new setting: "Receive emails from this test environment."
This option is located under Edit User > Preferences section > Checkbox: "Receive emails from this test environment."
This is disabled by default.
Enabling this feature allows you to enable emails in the Preview environment.
Emails from the Preview sandbox will have a subject of "Sandbox Preview message."