Exchange 2010 SP1 includes new code to throttle or manage connections from the Store Driver to mailbox servers as it delivers messages in such a way that Exchange can isolate and limit the effect of any faults that occur. Most of the time, you’ll be unaware that throttling applies to the Store Driver. However, if you receive non-delivery notification (NDR) messages that report problems from “STOREDRV” (the Store Driver), your Exchange hub transport servers might be hitting a limit.For example, an entry in Microsoft’s Exchange 2010 forum reports this error:
432 4.3.2 STOREDRV.Deliver; recipient thread limit exceeded
As a quick search for “STOREDRV 432″ reveals, the Store Driver issues a 432 NDR when it encounters other problems, so the important thing here is the text reporting that the “recipient thread limit exceeded”.
In most cases, the problem seems to be encountered with mailboxes that receive very heavy traffic such as those used for journaling. As you probably know, Exchange allows you to capture journal reports to any valid SMTP address. This facility allows you to direct journal traffic to a third-party journaling application but if you send journal reports to an Exchange mailbox, perhaps as an interim step before the reports are later moved to an archiving application, it’s possible that Exchange will encounter a throttle limit as the Store Driver attempts to deliver messages concurrently at times of peak demand. By default, Exchange 2010 SP1 will only attempt a single concurrent delivery to a mailbox to ensure that all of the mailboxes in a database receive a similar quality of service. This is what you’d want, but you can see that a journal mailbox might have many messages directed towards it concurrently.
The solution is to update the EdgeTransport.exe.config XML configuration file on the hub transport server to add two new keys to force Exchange to allow more than one concurrent delivery to a mailbox. Any text editor can be used to update the configuration file but it is best to update a test server first and measure the effectiveness of the change before you introduce it into production.
It is also best to make the update to all hub transport servers in the site that supports the journal mailbox so that the Store Driver has the same behaviour on all servers.
The new keys and their values are:
<add key="RecipientThreadLimit" value="2" />
<add key="MaxMailboxDeliveryPerMdbConnections" value="3" />
You should restart the Exchange Transport service after making the change to force the Store Driver to respect the new setting