SMTP Node Cannot Be Deleted or Copied

What causes this issue?

You attempted to delete the SMTP node. This is not possible. It is also
not possible to create more SMTP nodes. The SMTP node only exists once
in the system.

System Response

The node is not deleted.

How to fix this error?

If you do not want to use the SMTP node, deactivate the indicator 'Node
in use'. The node will then be deactivated and not used in the send
process.
You can reactivate the node at any time.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.