Knowledgebase

The performance issues may be caused by one or more of the following: 

• Insufficient computer specifications
• Absence of the latest service pack and updates for Outlook
• Large Personal Folders files (.pst) or Offline Folder files (.ost)
• Outlook .ost files or .pst files that are stored on a drive with insufficient write performance
• Third-party add-ins
• Your AppData folder is redirected to a network location
• Gadgets that access Outlook data (Windows Vista only)
• Microsoft Office Communicator integration
• Antivirus software interaction
• Windows Search or Windows Desktop Search indexing
• Incomplete closure of .pst files or .ost files
• POP3 accounts on Windows Vista clients
• Many Really Simple Syndication (RSS) feeds
• To-Do Bar and Online mode with Exchange server
• Damaged Outlook messaging profile

Does the computer meet the system requirements for the version of Office that you are using?

Make sure that the computer meets the system requirements for the version of Office that you are using. For more information about the system requirements for the Office, go the following Microsoft website appropriate for your version of Office:

For Office 2016 and Office 2013:

For Office 2010:


If the computer meets only the minimum system requirements, you will not experience optimal performance of Office.

Are you running the latest version of Outlook? 

We recommend that you install the latest applicable Service Packs (SP) and hotfix packages. For more information about the latest applicable updates, click the following article number to view the article in the Microsoft Knowledge Base:

Do you have a large .pst file or .ost file?

If you have a large .pst or .ost file, you may experience application pauses while you perform typical operations in Outlook. These typical operations include reading email messages, moving email messages, and deleting email messages. 

When you use Outlook, the following .ost size guidelines generally apply: 

• Up to 5 gigabytes (GB): This file size should provide a good user experience on most hardware.
• Between 5 and 10 GB: This file size is typically hardware dependent. Therefore, if you have a fast hard disk and lots of RAM, your experience will be better. However, slower hard disk drives, such as drives that are typically found on portable computers or early-generation solid-state drives (SSDs), experience some application pauses when the drives respond. 
• More than 10 GB: When the .ost file reaches this size, short pauses begin to occur on most hardware.
• Very large (25 GB or larger): An .ost file of this size increases the frequency of short pauses, especially while you are downloading new email messages. However, you can use Send/Receive groups to manually sync your mail. For more information about Send/Receive groups, see the "Are you synchronizing many RSS feeds?" section.

With Outlook 2010 and later versions, the maximum size for a .pst file is 50 GB. The default maximum size for a Unicode .pst or .ost file is approximately 25 GB. The following Microsoft Knowledge Base article describes how to increase the maximum size of a .pst or .ost file:

Are you running a computer that has a first-generation solid-state drive or a slow rotational hard disk drive?

If you are running Outlook on a computer that has a first generation solid state drive (SSD) or a slow rotational hard disk drive (HDD), you may experience frequent pauses when you perform typical operations in Outlook. 

Storing and retrieving data in an Outlook data file involves lots of small noncontiguous reads and writes. A good metric to use when you gauge data file performance on specific hardware is the disk drive’s noncontiguous write performance. The Windows performance team created the WinSAT tool. You can use this tool to benchmark specific disk drives.  

The WinSAT tool is included in Windows Vista and later versions of Windows. To run WinSAT, follow these steps:

1. Click Start, and then type cmd in the Search programs and files box. (Use the Start Search box in Windows Vista.)
2. Right-click cmd or cmd.exe in the results list, and then click Run as administrator. If you are prompted, enter your administrator credentials.
3. At the command prompt that appears, run the following command:
   
   Winsat disk -drive c -ran -write -count 10
   
   Note You can find the results in the following file:
   C:\Windows\Performance\Winsat\Winsat.log

The following table shows an estimated Outlook experience that is based on the score that is returned by the WinSAT tool.

Do you have many items in a single folder?

If you use .ost or .pst files

If you have lots of items in any single folder, you may experience performance issues during certain operations in Outlook while you use local data files. If you use Outlook to connect to a mailbox that is located on a Microsoft Exchange Server and use Cached Exchange Mode, Outlook synchronizes email and other items to an Offline Outlook Data (.ost) file. If you use Outlook to connect to other email accounts, such as POP3 or IMAP, Outlook stores email and other items to a local Outlook Data (.pst) file. These performance issues are especially noticeable when you switch into and out of folders that contain many items. 

If you have more than 100,000 items in a single folder in Outlook 2010 and later versions, views other than Arrange By: Date can be slower. We recommend that you move several items in these larger folders to separate folders in the same store or to an archive store and that you use Arrange By: Date when you run Outlook. For more information, click the following article number to view the article in the Microsoft Knowledge Base:  

If you connect to Exchange in Online mode

If you are not using Cached Exchange mode, you should review one of the following resources. These resources document some performance issues on an Exchange server that has high item counts and restricted views. Additionally, the resources discuss how these performance issues might affect the overall client user experience. For information about the performance effect of high item counts and restricted views, visit the following Microsoft web sites:

Do you have any nonessential add-ins or out-of-date add-ins installed in Outlook?

If you have nonessential add-ins installed, you may want to remove them from Outlook. To view the add-ins that are installed, follow these steps: 

1. In Outlook, click the File tab.
2. Click Options, and then click Add-ins to display a list of the COM add-ins that are installed.

By default, the following COM add-ins are included in Office 2010:

• Microsoft Access Outlook Add-in for Data Collection and Publishing
• Microsoft Exchange Add-in
• Microsoft Outlook Social Connector
• Microsoft SharePoint Workspace Proxy for Outlook Add-in
• Microsoft SharePoint Server Colleague Import Add-in
• Microsoft VBA for Outlook Add-in
• OneNote Notes about Outlook Items
• Windows Search Email Indexer

Any other add-ins that are listed under COM add-ins were installed by other software.

To determine whether the performance problem is caused by add-ins, run Outlook in safe mode. To do this, press and hold Ctrl when you start Outlook. When Outlook starts in safe mode, all COM add-ins and Exchange Server client extensions are disabled.

If the problem no longer occurs when Outlook is running in safe mode, it is likely that one of the add-ins is causing the performance issue. To troubleshoot possible problems that are caused by COM add-ins or Exchange Server client extensions, disable any items that you do not use regularly. Then, restart Outlook. If that does not resolve the problem, disable the remaining add-ins one by one. If that does not resolve the problem, the issue may not be caused by an add-in.

To disable COM add-ins, follow these steps: 

1. In Outlook, click the File tab.
2. Click Options, and then click Add-ins to display a list of the COM add-ins that are installed.
3. Select COM Add-ins in the Manage list, and then click Go.
4. In the COM Add-Ins dialog box, click to clear the check boxes for any COM add-ins that you want to disable.
5. Click OK, and then restart Outlook.

Is your AppData folder being redirected to a network location?

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.

Outlook stores certain data, such as email signatures and the spelling checker dictionary, in the AppData folder. If the network is performing slowly, Outlook must wait for read and write operations to the AppData directory to finish.

To disable redirection of the AppData directory, follow these steps:

1. Exit Outlook.
2. Start Registry Editor. To do this, use one of the following procedures, as appropriate for your version of Windows:
   
   • Windows 10, Windows 8.1 and Windows 8: Press Windows Key+R to open a Run dialog box. Type regedit.exe and then press OK.
   • Windows 7: Click Start, type regedit.exe in the search box, and then press Enter.
3. In Registry Editor, locate and then click the following subkey:
   
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
4. Locate and then double-click the following value:
   
   AppData
5. In the Value data box, type the following path, and then click OK.
   
   %USERPROFILE%\AppData\Roaming
   
   
6. Exit Registry Editor.

Did you install any gadgets that integrate with Outlook?

On a Windows Vista-based computer, remove any gadgets that you downloaded to display your Outlook data. This data may include the Outlook calendar, Outlook tasks, Outlook mail, and Outlook contacts. To remove gadgets on a Windows Vista-based computer, follow these steps:

1. Click Start, and then click Control Panel.
2. Click Control Panel Home.
3. Click Programs.
4. Click Windows Sidebar Properties.
5. In the Maintenance section, click
   View list of running gadgets.
6. Click any gadget that you want to disable, and then click
   Remove.

For more information about Windows Sidebar, view the "How do I customize Windows Sidebar?" Help topic in Windows Vista.

Is Outlook integration with Communicator enabled? Is Lync enabled?

By default, Outlook includes feature integration with Microsoft Office Communicator. The features that Outlook and Communicator share relate primarily to presence information such as whether someone is busy, away, or in a meeting. To disable feature integration, follow these steps: 

1. In Outlook, click the File tab, and then click Options.
2. Click Contacts, click to clear the Display online status next to a name check box under Online status and photographs, and then click OK.
3. Restart Outlook.

Is antivirus software running?

Warning This workaround may make a computer or a network more vulnerable to attack by malicious users or by malicious software such as viruses. We do not recommend this workaround but are providing this information so that you can implement this workaround at your own discretion. Use this workaround at your own risk.

If your antivirus software includes integration with Outlook, you may experience performance issues in Outlook. In this case, you can disable all Outlook integration within the antivirus software. Or, you can disable any antivirus software add-ins that are installed in Outlook. Be aware that if you are connecting to an Exchange Server mailbox, your mailbox or your email messages are already being scanned by antivirus software on the server. You should check with the Exchange administrator to make sure that this is the case.

You may have to contact the antivirus manufacturer to determine how to configure the antivirus software to exclude any integration with Outlook or to exclude scanning in Outlook.

Additionally, if you plan to perform file-level virus scanning while Outlook is being used, read the following Microsoft TechNet Library article.

Is Windows Search or Windows Desktop Search currently indexing data in the .pst or .ost file?

Windows Search in Windows 10 and Windows 8 or Windows Desktop Search (WDS) in Windows 7 and earlier versions indexes all data in .ost files and .pst files. However, the indexing of Outlook data occurs only when Outlook is running. Therefore, you may have to leave Outlook running overnight to determine whether performance issues are related to the building of your search indexes. 

Performance issues may increase when Outlook is running in online mode. Such performance issues occur because running Outlook in online mode increases the load on the Exchange server. This performance issue is especially noticeable when Outlook is configured in a nondefault state to index the items from the Exchange server to the local client index, and if more than one user indexes the Outlook data at the same time by using Windows Search or WDS.

To determine the indexing status for Outlook data in Outlook, follow these steps:

1. Click the search box above the list of email messages. The Search tab is enabled as soon as you do this.
2. In the Options section, click Search Tools, and then select Indexing Status.
3. In the Indexing Status dialog box, view the number of items that remain to be indexed.

The built-in back-off mechanisms in the indexing component of Windows Search or WDS pauses the indexing of Outlook data when the system is under heavy use. The easiest way to let the indexing finish is to leave Outlook running overnight.

Additionally, you can reduce performance issues by running Outlook in Cached Exchange Mode. In this mode, Windows Search or WDS searches the local copy of the mailbox instead of the mailbox content on the server.

Did the .pst file or the .ost file shut down incorrectly?

If the .pst file or the .ost file shuts down incorrectly, you may receive one of the following error messages the next time that you start Outlook: 

• Error message 1
  Outlook cannot open the data file
  filename until it has been checked for problems.
• Error message 2
  Microsoft Office Outlook’ exited without properly closing your Outlook data file ‘drive:\Users\username\AppData\Local\Microsoft\Outlook\outlook.ost’. ‘Microsoft Office Outlook’ must be restarted. If this error message recurs, contact support for ‘Microsoft Office Outlook’ for assistance.
• Error message 3
  The data file
  filename was not closed properly’. This file is being checked for problems.

If you receive one or more of these error messages, you may experience performance issues until Outlook finishes the reconciliation process for the .ost file or for the .pst file. The following gear icon appears in the status bar while Outlook checks the data file in the background: When this icon disappears, the .pst file or the .ost file is reconciled. The reconciliation process will pause at shutdown and resume (from where it was paused) the next time that you start Outlook.

An incorrectly shut down .ost file or .pst file may occur for one of the following reasons: 

• Antivirus scanning of the file
• Forced Microsoft Windows shutdown before the Outlook.exe process shuts down completely
• Outlook add-ins

If you see this issue frequently, and you must exit Outlook shortly before you shut down your computer, it may be better to shut down Windows while Outlook is still running. We recommend that you do this instead of exiting Outlook and then shutting down Windows shortly after that.

Do you use a rule that moves items out of the default store?

Rules that move items from the default store into another store can cause performance issues when Outlook downloads email messages.

If you are using rules to move mail from a POP3 account to another store, you can use new functionality in Outlook 2010 that lets you change the delivery location of the POP3 account. In this case, you do not have to use rules to deliver mail from that account to the separate store.

To do this, follow these steps:

1. In Outlook, click the File tab, click Info, click Account Settings, click Account Settings again, and then select the POP3 account in the list.
2. Click Change Folder at the bottom of the Account Settings dialog box to select a folder in the separate store to which you want to deliver that account.

If you do not use a POP3 account, you can also work around this issue by setting the target folder for all rules to be in the same Outlook store. Then, you can use the AutoArchive feature to move messages out of the default store in bulk.

For more information about how to configure the AutoArchive feature, click the following article number to view the article in the Microsoft Knowledge Base: 

Are you connected to a POP3 server?

For more information about a possible workaround if you are connected to a POP3 server and your download speeds are very slow, click the following article number to view the article in the Microsoft Knowledge Base:

Are you synchronizing many RSS feeds?

If you are synchronizing many RSS feeds into Outlook, you may experience performance issues when you perform certain ordinary operations. By default, all RSS feeds are synchronized automatically at set intervals. If you have too many feeds, Outlook may become unresponsive. 

You can create a separate Send/Receive group that contains only your RSS feeds, and you can remove them from the group in which your default mail account is located. This lets you sync the RSS feeds on demand instead of at set intervals. To do this, follow these steps:

1. Click the File tab, click Options, click Advanced, and then click Send/Receive in the Send and Receive section.
2. Click the All Accounts option, and then click Edit.
3. In the navigation pane (left side), click RSS.
4. Under Send/Receive Options, click to clear the check boxes next to the RSS that you do not want to synchronize with Outlook, and then click OK.
5. Click New, type a name for the new group, and then click OK.
6. Click RSS on the left side.
7. Select the RSS feeds that you want to limit, and then click OK.

The settings in the Send/Receive Group windows let you customize the synchronization rate of the new group.

Are you running Outlook with the To-Do Bar enabled or with a pinned peek when Outlook is running in online mode against an Exchange server? 

If you are running Outlook 2013 or later with a pinned peek or Outlook 2010 with the To-Do Bar enabled when Outlook is running in online mode against an Exchange server, the additional data that is displayed in the pinned peek or the To-Do Bar is retrieved from the server. Therefore, additional data requests for the pinned peek or the To-Do Bar are performed. These additional data requests cause additional network traffic that can affect the performance of some standard Outlook operations.

In Outlook 2010, the network traffic caused by the To-Do Bar is reduced from what it was in earlier versions, especially when the To-Do Bar is loading recurring calendar items.

To avoid additional network traffic and the resulting performance effect in Outlook, you can remove the peek or turn off the To-Do Bar and therefore reduce the network traffic between Outlook and Exchange in online mode. This reduction in data retrieval requests affects the user experience most significantly if you have a network that has high latency or limited bandwidth. 

To remove the Peek or turn off the To-Do Bar in Outlook, click To-Do Baron the View menu, and then click Off.


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.

Administrators can disable the To-Do Bar on users’ computers running Outlook 2010 by using the following registry information.

If you do not use a policy setting, use the following information.

Registry location: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Options\ToDoBaror 
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\Options\ToDoBar
Value name: DisableToDoBar
Value type: DWORD
Value data: 1 or 0

Note If the value data is set to 1, the To-Do Bar is turned off. If the value data is set to 0, the To-Do Bar is turned on.

For more information about how administrators can control the user interface through policy settings, go to the following Microsoft websites:

Have you tried to create a new Outlook profile?

In some cases, an Outlook messaging profile may be misconfigured. Creating a new Outlook profile may resolve some performance issues. For more information about how to create a new Outlook profile, click the following article number to view the article in the Microsoft Knowledge Base: