Event ID 9646 is logged in the application event log of your Exchange Server 2003 computer when a client opens many MAPI sessions

On a server that is running Microsoft Exchange Server 2003, an event that resembles the following event is logged in the Application log:

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".

When this issue occurs, you may also receive the following error message in Microsoft Office Outlook 2003:

This issue may occur if the following conditions are true:

• You have installed Microsoft Exchange Server 2003 Service Pack 1 (SP1) on the Exchange Server computer.
• A program that is running on a client computer opens many MAPI sessions to the Exchange Server computer. The number of MAPI sessions is larger than the permitted limit.
• You are using Microsoft Office Outlook 2007, and you add a large additional mailbox to your profile. For example, this issue may occur if the additional mailbox contains more than one thousand folders.

Exchange Server 2003 SP1 imposes a restriction on the number of permitted MAPI sessions per user. By default, the maximum number of permitted MAPI sessions per user is set to a hexadecimal value of 0x20 after you apply Exchange Server 2003 SP1.

Note A hexadecimal value of 0x20 converts to a decimal value of 32.

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.

1. On the Tools menu, click Account Settings.
2. Click the Exchange Server account, and then click Change.
3. Click More Settings.
4. On the Advanced tab, click to clear the Download shared folders (excludes mail folders) check box.
5. 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:

1. 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.
2. Click the Security tab.
3. 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.
4. Under the Allow column, click to select the View information store status check box, if this check box is not already selected.
5. 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.

If this issue occurs after you install the Scalable Networking pack or Windows 2003 Service Pack 2, see the following article in the Microsoft Knowledge Base:

To change the value of the maximum permitted MAPI sessions per user from the default, you can configure the Maximum Allowed Sessions Per User registry entry. To do this, follow these steps.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
3. If the Maximum Allowed Sessions Per User entry does not exist, do the following:
   1. On the Edit menu, point to New, and then click DWORD Value.
   2. Type Maximum Allowed Sessions Per User as the entry name, and then press ENTER.
4. Right-click the Maximum Allowed Sessions Per User entry, and then click Modify.
5. Click Decimal, type the value that you want to set in the Value data box, and then click OK.
6. Exit Registry Editor.
7. Click Start, click Run, type services.msc in the Open box, and then click OK.
8. Click the MSExchange Information Store service, and then click Restart Service.