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I came across this error while I(or my users) trying to restore bulk emails in outlook using “Recover Deleted Items” option. Single or little more emails restoration works fine but this issue is coming only when I attempt bulk restoration.
When this happened for the user, I am clue less what was happening. I went to event viewer on the server where user mailbox is hosted and observed below error when the user is attempting the restoration.
Event Type: Error
Event Source: MSExchangeIS
Event Category: General
Event ID: 9646
Time: 3:45:47 PM
Mapi session “/o=ORG/ou=SITE/cn=Recipients/cn=myuser” exceeded the maximum of 500 objects of type “objtFolder”.
After a little bit of googling I found an article (http://support.microsoft.com/kb/830829/en-us) which is talking about similar issue and increasing the limits on Object types that you see in event viewer should fix the issue. I tried increasing the ObjFolder limit to 1000(note: 500 is the default; if you don’t find this key, it is safe to create one as per KB) on my exchange server but still it didn’t work and was saying exceeded the limit of 1000 this time. At this point I was not sure what was the optimum value to which I should increase this limit to make the restoration happen. As I didn’t find answer to this question in google, I polled one of friend who is with MS and knows more about exchange. He said there are no limits defined as such and it’s a trial and error method we should try. I bumped it to 10,000 this time and restoration worked. Along with this informaiton, my friend passed me a note as well. The more limit you put the more the load on your exchange server. So, be cautious while increasing the limits and I prefer to do it during off hours so that load will be less on the server and your users will be away anyways and that also gives you ample time to troubleshoot any unforeseen issues.
Additional note: While trying this you might see events about exceeding the limits of other object types described in aforementioned KB. You should create necessary registry keys for them as well to make your restoration suceessfull. Don’t forget to revert your settings once you are done with restoration; otherwise it will impact your server performance. Generally this will come into effect after store restart. Otherwise you can wait for 15-30 mins to make store pick these changes without restarting the IS.
Hope this information helps you.