The "Export to Excel by Email" button is not a default system command — it is actually a custom button that was added to the entity’s command bar within the solution. That’s why it doesn’t appear in the standard Ribbon Workbench view unless you're editing the correct solution component where the customization was made.

To manage or remove it, open the solution where the entity is customized, navigate to the command bar for that entity, and you should see the button listed there. From there, you can apply display rules, remove it, or modify its behavior as needed.