Memory or performance problems looping through items

You use the Outlook object model to loop through items in a folder, but run into memory limitations, or the amount of time that it takes to process an item increases as the collection of items is processed.

The items are based on a custom form that uses Microsoft Visual Basic Scripting Edition (VBScript), and Outlook does not release memory related to VBScript until the entire collection of items is processed.

You can add a registry key to limit the number of times that Outlook loads the VBScript code.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.


Create the following DWORD registry key based on your version of Outlook, and set the value to a number that is larger than 0.

Outlook 2002 Outlook 2003 Outlook 2007 Outlook limits the number of simultaneous script objects to that number. You can set it to any small number, which allows most looping scenarios to run. However, Microsoft recommends you set it to a value in the range of 10 to 20 because after you implement this registry key, custom forms that are opened through the Outlook user interface are also affected. For example, if you set the value to 2, and then open three custom forms with VBScript in them, the VBScript code will not run in the third item you open.

Depending on what types of items that you are processing and what fields you need to access, you may be able to use the Collaboration Data Objects (CDO) object model to access the items instead of the Outlook object model.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

Steps to Reproduce Problem

NOTE: Use a Microsoft Window NT or Microsoft Windows 2000-based computer so that you can later see memory usage by using the Windows Task Manager.

1. Create a custom contact form in your default Contacts folder, and then add a custom command button to it.
2. Add the following VBScript code:

   Sub CommandButton1_Click()
      ' Get a reference to the default contacts folder
      Set objFolder = GetNamespace("MAPI").GetDefaultFolder(10)
      MsgBox "Start loop"
      For i = 1 to objFolder.Items.Count
         Set objItm = objFolder.Items(i)
         ' After this assignment, the memory is allocated
         strTemp = objItm.Fullname
         ' if objItm contains no VBScript code, it is freed here 
         Set objItm = Nothing 
         Set strTemp = Nothing
      Next
      MsgBox "Loop ended successfully."
   End Sub
   					

3. Create several hundred items in the folder based on the custom form.
4. Open one of the items, and then click the command button to run the code.
5. Open the Windows Task Manager, and you should see Outlook memory usage increasing.

For additional information about available resources and answersto commonly asked questions about Microsoft Outlook solutions, click the article number below to view the article in the Microsoft Knowledge Base: