How to Resolve Event ID 9646 Closing Mapi session "/o=Organization/ou=Administrative Group/cn=Recipients/cn=Recipient" because it exceeded the maximum

Event Type: Error
Event Source: MSExchangeIS
Event Category: General
Event ID: 9646
Description:
Closing Mapi session "/o=Organization/ou=Administrative Group/cn=Recipients/cn=Recipient" because it exceeded the maximum of 32 objects of type "session".

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To resolve this issue, we recommend that you first determine whether the MAPI session limit is reached because of potential abuse, because a large additional mailbox was added, because it is the result of a bug in a client program, or because of client program design.

If the issue occurs because a large mailbox was added to a Cached Exchange Mode profile in Outlook 2007, you can disable the new Outlook 2007 default feature that causes this issue. To do this, follow these steps.

Note When you follow these steps, you cannot access the shared mailbox folders while you are working offline by using your Cached Exchange Mode profile.
On the Tools menu, click Account Settings.
Click the Exchange Server account, and then click Change.
Click More Settings.
On the Advanced tab, click to clear the Download shared folders (excludes mail folders) check box.
Click OK, click Next, and then click Finish.
If the issue occurs because of a bug in a client program or because of client program design, we recommend that you contact the vendor to determine whether you can use one of the following procedures:
Obtain a fix
Grant View Information Store Status permissions to the account under which the program runs

Note Programs that run under an account that has these permissions are not affected by the MAPI sessions-per-user limit.
To grant View Information Store Status permissions, follow these steps:
In Exchange System Manager, right-click the Exchange Server object or the mailbox store to which you want to grant the permissions, and then click Properties.
Click the Security tab.
Click the account to which you want to grant the permissions.

If the account is not listed, click Add, click the account name, click Add, and then click OK.
Under the Allow column, click to select the View information store status check box, if this check box is not already selected.
Click to clear the check boxes for any permissions that are not required, and then click OK.

Note You may have to follow this step if you clicked Add to add the account in step 3. This is because every check box in the Allow column was selected when you added the account in step 3.
If you cannot obtain a fix, and if you cannot configure the account to run together with View Information Store Status permissions, you can adjust the number of MAPI sessions per user that are permitted by configuring the registry settings. If you do this, try to determine the minimum value that you can use so that the client program can run without problems. If you raise the limit too high, the client program might affect the performance of the Exchange Server computer.

Source: http://support.microsoft.com/kb/842022