This constant determines whether synchronization via a mutex object is enabled for mailbox objects. When this constant is set to 1, the feature is enabled; when set to 0, it is disabled. The default value is 1. In cases where OS_MBOX_PEEK_FUNC is set to 0, OS_MBOX_PROTECT_MUTEX must also be set to 0. If this feature is not required, it may be disabled to reduce the final code size. For further details, please refer to the mailbox objects section.