Message Volume

When a new message is delivered or created, the message is saved in the current message volume. Additional message volumes can be created, but only one is configured as the current volume where new messages are stored. When the volume is full, you can configure a new current message volume. The current message volume receives all new messages. New messages are never stored in the previous volume.

A current volume cannot be deleted, and message volumes that have messages referencing the volume cannot be deleted
Specifically

A current volume cannot be deleted, and message volumes that have messages referencing the volume cannot be deleted
Does cannot mean -
Will not be permitted by the system?
or
Would be a really really bad idea?