Today I got to chat with a colleague who was trying to troubleshoot a weird Exchange public folder replication problem. The environment, which is the middle of an Exchange 2007 to Exchange 2010 migration, uses public folders heavily – many hundreds of top-level public folders with a lot of sub-folders. Many of these public folders are mail-enabled.
After replicating creating public folder replicas on Exchange 2010 public folder databases and ensuring that the public folders were starting to replicate, my colleague received notice that specific mail-enabled public folders weren’t getting incoming mail content. Lo and behold, the HT queues were full of thousands of public folder replication messages, all queued up.
After looking at the event logs and turning up the logging levels, my colleague noticed that they were seeing a lot of the 4.3.2 STOREDRV.Deliver; recipient thread limit exceeded error message mentioned in the Microsoft Exchange team blog post Store Driver Fault Isolation Improvements in Exchange 2010 SP1. Adding the RecipientThreadLimit key and setting it to a higher level helped temporarily, but soon the queues would begin backing up again.
At that point, my colleague called me for some suggestions. We talked over a bunch of things to check and troubleshooting trees to follow depending on what he found. Earlier tonight, I got an email confirming the root cause was identified. I was not surprised to find out that the cause turned out to be something relatively basic. Instead of just telling you what it was though, I want you to tell me which of the following options YOU think it is. I’ll follow up with the answer on Monday, 10/15.