Started yesterday morning but is getting progressively worse. The queue which sends mail to the journal mailbox seems to be processing email, just not fast enough, so the queue continues to get bigger and bigger. No changes were made yesterday. Five servers in a DAG, all Exchange 2013 (CU4). Besides the obvious, "update to CU7 or CU8", does anyone have any

The majority of the messages sitting in the queue have the following error:

432 4.3.2 STOREDRV.Deliver; recipient thread limit exceeded

I found the following two articles which reference this issue on Exchange 2010 Hub Transport servers, but they reference modifying the 'edgetransport.exe.config' file.

http://blogs.technet.com/b/exchange/archive/2011/04/11/store-driver-fault-isolation-improvements-in-exchange-2010-sp1.aspx

https://social.technet.microsoft.com/Forums/en-US/022acffe-d80d-4fd6-8c01-2bc5f020ec91/432-432-storedrvdeliver-recipient-thread-limit-exceeded-in-the-queue-of-mails-exchange-2010?forum=exchange2010

Opened a support ticket with MS; I'll post a follow-up tomorrow with the proposed resolution steps and what the outcome was.

Hi,

Please check whether there is any third-party program installed in your Exchange server. Please disable it and reboot your server to have a try. Glad to wait for your solution sharing from Microsoft side :)

Regards,

There is no 3rd party software on the Exchange servers, only MS products (Exchange and pre-reqs, Lync items, DPM agent and SCOM agent). With assistance from support, the MSExchangeDelivery.exe.config file was modified with additional keys entered, and I changed the "MaxConcurrentMailboxDeliveries " value from 20 to 100 in the 'mailbox transport service' and 'transport service', then restarted the 'mailbox transport delivery' and 'transport' services. At the time of the changes, the queue had exceeded 50k messages; it is currently hovering between 10k and 12k.

UPDATE:The journal mailbox, or the DB it was in, was suspected to have been corrupted or contain corrupted emails.  I created a new DB with a new journal mailbox and mail is flowing as expected.  The old journal mailbox is being moved to a new DB now, and I'm filtering for bad items to try and remove any corruption.