How to Reset Exchange 2010 MWI

Exchange 2010 has native message waiting indicator (MWI) support.  This feature enables the MWI light on your business phone when you receive a new voicemail in Exchange 2010 Unified Messaging (UM).  When a voicemail is received by the UM server it sends a SIP command to the PBX to tell it to turn the MWI on.  MSExchange Unified Messaging event 1343 is logged if diagnostic logging is turned up on the Exchange 2010 UM server:

(BTW, have I ever mentioned how much I hate typos in event logs?  Succesfully?  Really?)

Exchange 2010 reads the Voice Mail search folder to know if there are any unread voicemail messages.  If there are, it sends the SIP message above.  Simply marking a voicemail as unread should enable the MWI and cause the event to be logged.

The Voice Mail search folder is created when you UM enable a mailbox.  Exchange Web Services (EWS) is responsible for creating this search folder.

Sometimes Exchange 2010 is unable to read the Voice Mail search folder due to corruption.  I've seen this happen when mailboxes are migrated from Exchange 2007, which has no native MWI support, and third-party MWI software is used, such as Geomant MWI for Microsoft Unified Messaging.  In this case you need to delete and recreate the Voice Mail search folder from Outlook.

Note: You cannot delete the Voice Mail search folder using OWA since it treats it as a protected folder.  You must delete it using Outlook 2007 or 2010.

But what happens if you delete the Voice Mail search folder?  Well, bad things happen in MWI land.  You'll notice that there are no 1343 events logged for that user anymore and the MWI light will not change.  If it was on, it stays on.  If it was off, it stays off.  The fix is to have EWS recreate the folder.  You cannot create this special search folder manually, you need EWS to do it.

David Sterling, a Senior Software Development Engineer on the Microsoft Exchange Web Services Team, wrote an excellent post about the Voice Mail search folder and how to recreate it.  Fellow MCM Keif Machado and I spent quite a while trying to get it to work at a customer before we discovered that it only works in Exchange online mode.

Here are the steps to delete and recreate the Voice Mail search folder to fix MWI:

1. Make sure that Outlook is running in online mode (Not Cached Exchange Mode).  In online mode Outlook will say "Online with Microsoft Exchange" in the status bar, not "Connected with Microsoft Exchange".
2. Delete the Voice Mail search folder in Outlook.  This only deletes the search folder, not the messages.
3. Dial into Outlook Voice Access to access your old voicemails.  You need to enter the "voice mail" command, even if OVA says you have no new voicemails.  When you do this, EWS will recreate the Voice Mail search folder in Outlook.  Hang up.
4. Reconfigure Outlook to use Cached Exchange Mode again and restart Outlook.  Since the OST header still matches the mailbox database header, Outlook will use the same OST and will resync your emails quickly and easily.

Now test MWI functionality by marking voicemails as unread in the Voice Mail search folder and by leaving a new voicemail.