Performance and synchronization problems when you work with folders in a secondary mailbox in Outlook

For Outlook for Office 365

Lift the 500 shared folders limitation in Outlook

The synchronization of the shared folders is improved so that Outlook will no longer encounter the 500 shared folders limitation, and Outlook should be able to accommodate up to 5,000 shared folders. The new functional limit will vary by Outlook's available resources and system configuration. These changes were released to the Office Monthly (Targeted) channel with the version1904 release, to the Office Monthly Channel with the version 1905 (Build 11629.20196) release and later. And they will be included in Semi-Annual channel releases on the regular Semi-Annual schedule (September 2019 for Semi-Annual Channel (Targeted) and January 2020 for general release). For more information, see Lifting the 500 Folder Limit in Outlook.

For Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010 and Outlook 2007

To resolve this problem, use one of the following methods.

Important
Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.

Method 1: Reduce the number of folders in the Shared mailbox

The best solution to this issue is to reduce the number of mail folders in the shared mailbox, especially if your mailboxes are in the Office 365 environment. Additional methods 2 and 3 in this article advise you to turn off the caching of mail folders or all folders in the shared mailbox. These solutions do work, but it is recommended to keep caching enabled for Office 365 mailboxes and mailboxes on a slow network. For more information, see the following article:

Method 2: Disable caching of all shared folders

Outlook 2010 and later versions

To disable the caching of all shared folders in Outlook 2010 and later versions, follow these steps:

1. On the File tab, click Account Settings in the Account Settings list.
2. In the Account Settings dialog box, click the E-mail tab and then double-click your Microsoft Exchange Server account.
3. In the Change Account dialog box, click More Settings.
4. In the Microsoft Exchange dialog box, click the Advanced tab.
5. Click to clear the Download shared folders check box.
   
   
    
6. Click OK two times.
7. Click Next, click Finish, and then click Close.
8. Restart Outlook.

Outlook 2007

To disable the caching of all shared folders in Outlook 2007, follow these steps:

1. On the Tools menu, click Account Settings.
2. In the Account Settings dialog box, click the E-mail tab and then double-click your Microsoft Exchange Server account.
3. In the Change Account dialog box, click More Settings.
4. In the Microsoft Exchange dialog box, click the Advanced tab.
5. Click to clear the Download shared folders check box.
   
   
    
6. Click OK two times.
7. Click Next, click Finish, and then click Close.
8. Restart Outlook.

After you make this change, none of the shared folders in the secondary mailbox will be available to you in Outlook when you are working offline. However, all folders in the primary mailbox will still be available to you when you are working offline.

For more information about how to disable the download shared folders by using a Group Policy setting, click the following article number to go to the article in the Microsoft Knowledge Base:

Method 3: Change the configuration of the secondary Exchange mailbox to a second Exchange account in your profile

Outlook 2010 and later versions only

If you want to cache all folders in the secondary Exchange mailbox, follow these steps to modify your Outlook profile so that the secondary mailbox is added as a second Exchange account.

Note To follow these steps, you must either know the password for the account of the secondary mailbox or you must have full mailbox permissions to the account for the secondary mailbox. See your Exchange Server administrator for this information or permissions.

1. Make sure that automapping is disabled for the secondary mailbox. For more information, see the following Microsoft Knowledge Base article:
   2646504 How to remove automapping for a shared mailbox in Office 365
2. On the File tab, click Account Settings in the Account Settings list.
3. In the Account Settings dialog box, click the E-mail tab, and then double-click your Microsoft Exchange Server account.
4. In the Change Account dialog box, click More Settings.
5. In the Microsoft Exchange dialog box, click the Advanced tab.
6. Click the Advanced tab. In the Mailboxes section, select the secondary mailbox, and then click Remove.
7. Click Yes when you are prompted to confirm the removal of the mailbox.
8. Click OK, click Next, click Finish, and then click Close.
   
   Note At this point, the secondary Exchange mailbox is no longer associated with your Outlook profile.
9. Exit Outlook.
10. Open the Mail item in Control Panel.
11. Select your profile, and then click Properties.
12. Click E-mail Accounts.
13. On the E-mail tab of the Account Settings dialog box, click New.
14. In the Choose Service section of the Add New Account dialog box, click E-mail Account, and then click Next.
    
    If you know the password for the secondary mailbox account, go to step 14.
    
    If you do not know the password for the secondary mailbox account, but your account has full mailbox permissions to this secondary mailbox, go to step 18.
15. In the Auto Account Setup section of the Add New Account dialog box, enter the following account information for the secondary mailbox, and then click Next.
    Name
    Email address
    Password
     
    
     
16. After the account has successfully been configured, click Finish.
17. Click Close, click Close, and then click OK.
18. Go to step 22.
19. In the Auto Account Setup section of the Add New Account dialog box, click Manually configure server settings or additional server types, and then click Next.
20. In the Choose Service section of the Add New Account dialog box, click Microsoft Exchange or compatible service, and then click Next.
21. In the Server Settings section of the Add New Account dialog box, enter the following information for the secondary mailbox, and then click Next.
     
    Server (this is the Exchange server name)
    Use Cached Exchange Mode (enabled to allow the secondary mailbox to be cached locally in your .ost file)
    User name
    
    
22. Click Finish, click Close, click Close, and then click OK.
23. Start Outlook.

Note If your account does not have full mailbox permissions to the secondary mailbox, you are prompted for the account credentials to the secondary mailbox. You may experience the following specific issues when you use Outlook after you make the configuration changes that are specified in this method.
 

• New email alerts are displayed for both Exchange mailboxes.
  
  

• Messages that are marked as private can be viewed in the second Exchange mailbox even though the account of the first Exchange mailbox is not configured specifically to allow for the viewing of private messages.