Cannot change the default Mail Message form

If you create a custom Microsoft Outlook 97 form based on the Mail Message form, when you try to set the custom form as the default form for the Inbox, you may receive the following error message:

The base message class (an internal property) of the custom form does not match the Inbox folder's base message class.

Microsoft Outlook 2000 and Outlook 2002 allow you to directly change the default mail message form. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Use one of the following approaches to work around this limitation:

1. Publish the form and then open it when you want to use it. For more information about where to publish the form, click the following article number to view the article in the Microsoft Knowledge Base:
   264117  (http://support.microsoft.com/kb/264117/ ) How to determine where to publish a form
   To publish the form in the Inbox Folder Forms Library, follow these steps:
   1. With the custom form open, on the File menu, click Publish Form As.
   2. In the Publish Form As dialog box, click Publish In.
   3. From the Folder Forms Library list, select Inbox.
   4. Click OK, and then click OK again. To use the form, on the Compose menu, click New <form name>, where <form name> is the name of the form that you just published.
2. If you want to programmatically maniupulate incoming mail messages, there is no way to have a custom form applied to incoming mail, so you cannot use Visual Basic Scripting Edition (VBScript) code in a custom Outlook form to do this. All mail that is received will have a message class of IPM.Note and will use Outlook's default mail message form. For this scenario, use one of the following approaches:
   • Create a separate program that runs continuously (an "agent") and periodically automates Outlook to process new items in the Inbox. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
     281111  (http://support.microsoft.com/kb/281111/ ) How to create a solution that runs at a specific time interval
   • If you can program using the C/C++ language, create an Exchange Client Extension, which can manipulate incoming mail message.
     http://msdn2.microsoft.com/en-us/library/Aa483711.aspx (http://msdn2.microsoft.com/en-us/library/Aa483711.aspx)

To set a default form for a folder, follow these steps:

1. Using the right mouse button, click the folder, and then click Properties on the shortcut menu.
2. Click the General tab, and specify the default form by selecting the "When posting to this folder, use" choice.

If the base message class of the custom form and the folder type do not match, you will receive the error message mentioned in the "Symptoms" section of this article. The base message class of the form and the folder must match before you can set the form as the default form.

The table below lists the folder type and its message class. When creating a custom form based on the Mail Message form, the base message class is IPM.Note. This base message class is not one of the classes that you can set as default; therefore, you cannot set a custom Mail Message form as default for any of these Outlook folders.

For folders other than mail item folders, this is not limiting behavior. If you are designing a custom form for a Task folder, you start with the built-in Task form which has the IPM.Task message class; therefore, the base message class is compatible. The only folder type that has this limitation is the Mail Items folder type.

For more information about creating solutions with Microsoft Outlook 97, click the following article number to view the article in the Microsoft Knowledge Base: