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Question
Tuesday, October 29, 2013 5:53 PM
We've been experiencing an issue for the last week where users cannot access their mailboxes because of too many Mapi sessions. A few weeks back we upgraded from Exchange SP2 to SP3. We have 1 CAS server and 1 Mailbox server. This happens about twice a day and the Information Store needs restarted for users to connect again.
Errors on the CAS are:
Process Microsoft.Exchange.InfoWorker.Common.Delayed`1[System.String]: MailTips query failed for mailbox <User_Redacted>. Latency: total:10. The returned exception is: Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException: Cannot open mailbox /o=<Org_Redacted>/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=<Server_Name>/cn=Microsoft System Attendant. > Microsoft.Mapi.MapiExceptionSessionLimit: MapiExceptionSessionLimit: Unable to open message store. (hr=0x80040112, ec=1246)
Error on the Mailbox Server
The Message Waiting Indicator Assistant was unable to obtain the MWI state for mailbox '<User_Redacted>(8d7a5a8b-c83d-49fe-9190-269c867676c6)' on database '<Database_Name> (9eaa06b5-2949-42c2-99b1-4496f3c50364)'. You can safely ignore this warning if the mailbox is currently disconnected or inactive. Additional information: Microsoft.Exchange.Data.Storage.TooManyObjectsOpenedException: Cannot open mailbox /o=<Org_Redacted>/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=<Server_Name>/cn=Microsoft System Attendant. > Microsoft.Mapi.MapiExceptionSessionLimit: MapiExceptionSessionLimit: Unable to make connection to the server. (hr=0x80040112, ec=1246)
I have tried creating the following registry keys under HKLM\SYSTEM\CurrentControlSet\services\MSExchangeIS\ParamatersSystem on the Mailbox Server:
Maximum Allowed Concurrent Exchange Sessions Per Service = 250000
Maximum Allowed Exchange Sessions Per Service = 450000
Maximum Allowed Service Sessions Per User = 500000
Maximum Allowed Sessions Per User = 500000
I understand that those values are high, they started as default and I've raised them each time the problem occurred, hoping that it would help alleviate this issue. I'm running out of ideas and can't keep rebooting the IS twice a day.
All replies (3)
Wednesday, October 30, 2013 10:20 AM ✅Answered
Hi Shawn,
From your description, there are too many Mapi sessions. So I recommend you configure a CAS array to troubleshoot the issue.
Here are some threads about CAS array for your reference.
Microsoft Exchange 2010 CAS Array – Steps and Recommendations
Exchange 2010–Links to how to setup CAS Array with a Load Balancer
Besides, you can use Windows Performance Monitor to examine how programs you run affect your computer's performance.
Hope it helps.
Best regards,
Amy
Wednesday, October 30, 2013 1:13 PM
Hi Shawn,
can you check if Throttling polcy can help you on this
Exchange 2010 Client Access Throttling.
http://blogs.msdn.com/b/pepeedu/archive/2010/01/13/exchange-2010-client-access-throttling.aspx
http://techbridle.blogspot.in/2011/06/increasing-mapi-concurency-connections.html
Tuesday, November 5, 2013 1:54 PM
I was able to find a resolution for this issue. Through packet captures, we found that a Hyper-V host was flooding the network, causing the CAS server to ask for clients to resend packets. This caused them to create new sessions which quickly exceeded the limits. We have taken down the troubling host and sessions are back under 20,000.