Detected indexing backlog for multiple databases on server

hello,

  I am getting an error in my SCOM Alerts.we are  using Exchange 2010 and scom 2012 RTM.

Indexing backlog reached a critical limit of 48 hours or the number of items in the retry queue is greater than 10000 for one or more databases: DB1 (7, 14332, 0)
EventSourceName: CI Troubleshooter.

please help me if any one have knowledge about it,

Thank you!