The set of folders cannot be opened Your server administrator has limited the number of items you can open simultaneously

In Outlook 2010 (Exchange 2010) Configured with multiple Mailboxes received error while accessing Mailbox's

"The set of folders cannot be opened. Your server administrator has limited the number of items you can open simultaneously."

In the Event log, Application log on Mailbox server

Error General 9646 MSExchangeIS ExchangeFQDN.domainname.com N/A Mapi session b07d8c58-536d-4e6c-80b2-cd6722433802: /O=ORG/OU=OU/cn=Recipients/cn=Recipientsname" exceeded the maximum of 32 objects of type "session"."

Things need to check

@Outlook

1. Check for 3rd party Add-in to Ms Outlook

. If Outlook is configured in Cached Exchange mode.

. Open Outlook in “Folder list” module on the Navigation Pane to see \Sync Issues

* 2. Check if firewall is causing any connection timeout. (RPC timeout)

check this link New Best Practice for RPC Timeouts in Exchange

3. Check Perfomrance at MBX SERVER

4. Disable TCP Chimney, RSS on Exchange server, if networking is an issue, also confirm with EXBPA

Possible Resolution

1. In Outlook Profile if secondary Mailbox or more Mailboxes added, try removing Mailbox from Outlook Profile. If fewer number of Mailboxes are added then try checking the Mailboxes folder.

*2. Also check for Shared Mailbox if it is enabled, if it is enabled disable it.

To disable Caching of shared folders in Outlook 2010/2013

File > Account Settings > Account setting lists > E-mail tab > "double click" Exchange server Account > in Change account > More settings > Advanced tab > click to clear "Download shared folders" > finish and complete the Wizard and restart the Outlook.

3. If still you want to Cache Shared folders in the secondary Exchange mailbox, remove secondary Mailbox from Account settings and Open Mail item in control panel and Add new account.

4. Check if firewall is between Outlook client and Exchange and causing RPC reset *

5. Here Event id 9646, indicates towards, "Session" limit, so try increasing session value but it may effect Server's performance, increase session size in +3

6. MAPI session Limit disabled 

From Registry Editor (always have backup of Registry key*), goto the location

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSexchangeIS\ParametersSystem

If value "Disable Session Limit" exist then change the value to 1 (Dec) from 0 or else create a new DWORD KEY.