We experienced an issue recent in a Exchange 2010 environment where all public folder replications messages were stuck in the queue on one of our Exchange boxes with the following error “432 4.3.2 STOREDRV.Deliver; recipient thread limit exceeded”.
After looking into this for a while i came across the following article “http://blogs.technet.com/b/exchange/archive/2011/04/11/store-driver-fault-isolation-improvements-in-exchange-2010-sp1.aspx” which explains the reasons why the following problems occurring since the changes in Exchange 2010 Sp1.
To Resolve the issue we added the following text to the edgetransport.exe.config file.
<add key="RecipientThreadLimit" value="2" />
<add key="MaxMailboxDeliveryPerMdbConnections" value="3" />
After adding the key and restarting the Hub Transport service to apply the setting all queues emptied and messages got sent