Question : Back Pressure Exchange 2007 SP1

We're no longer able to receive external emails, however we can send out and receive internally.  This is an existing setup, as the problem just started a few days ago.  We have two sites:  each has 1 mailbox server and 1 Hub/CAS server.  Both sites are affected.  I noticed an event 15004 error on each Hub/CAS server.  It stated version buckets high.  It was 563.  Other thresholds for the queue databases were normal.  Per the following article, I increased the databasemaxsize cache to 512MB, but the problem continues.  http://msexchangeteam.com/archive/2008/05/14/448890.aspx.

I need help ASAP as this is affecting our production environment.

Answer : Back Pressure Exchange 2007 SP1

Problem resolved.  Applied changes recommended in this article:  http://msexchangeteam.com/archive/2009/07/07/451737.aspx