Controlled by Permission Set Behavior on Email-to-Case Routing Address

When the Controlled by Permission Set checkbox is enabled on an Email-to-Case routing address, Salesforce Lightning Experience enforces access to that routing address via a permission set. Users must be assigned a permission set that explicitly grants access to the routing address in order to use it when sending emails from Cases. This enforcement applies to Lightning Experience only — Classic does not enforce this checkbox.

Real-life example: An administrator enables the "Controlled by Permission Set" checkbox on a routing address used by the support team. A support agent who does not have the corresponding permission set assigned will no longer see that routing address as an available option when composing an email from a Case in Lightning Experience — even though the same agent can still use the routing address in Salesforce Classic. This inconsistency can cause confusion for agents who switch between interfaces.