9696d660_Exchange_Voice_Mail_User_Guide__Description
[Feature] Full mailbox notification [How to Enable or Disable] When your mailbox is full, you will not receive voice mails messages on your phone, nor will they be forwarded to email. Once old messages are deleted, any new voice mails will appear. See the Voice Mail Over-Quota Mailbox Policy [Description] 
Indicates when you are approaching a full Exchange mailbox
ITS Exchange Voice Mail User Guide
Description