Thursday 14 June 2007

Forms and Outlook item types

Regardless of whether your Outlook data is stored on an Exchange Server or in a PST file, all of your Mail, Calendar, Task, Contact and other items are stored in messages.

The fact we can see different types of item (appointments, tasks, etc.) seems to contradict this, but the messaging system that underlies Outlook deals in messages and nothing else. We see messages with different properties, being displayed in different forms.

If you use a tool such as MFCMAPI or MDBVU (the usual disclaimer applies) to look at an item's properties, you will see the PR_MESSAGE_CLASS property for a mail item is set to ipm.note, where a calendar item would be ipm.appointment. Outlook opens the correct form (a form is a defined layout for displaying an item) depending on the PR_MESSAGE_CLASS which is how your calendar appointments get scheduling information displayed and your mail items don't.

Outlook has a form associated with each folder - whether it's one of the default folders (Inbox, Calendar, Tasks, etc.) or one you created. Each folder is associated with a message type, and also with a form to go along with it. So if you wanted to create a custom form to show different information for the contacts in your Mobile Contacts folder, you could do that.

A common scenario to troubleshoot in a large corporate environment is where a user is unable to open items of a certain type, or where items of a certain type don't behave as they should (e.g. a button on the form doesn't work). Outlook caches custom forms to save loading them each time they are used, and sometimes this cache can become corrupt, so clearing the forms cache is a logical early step when dealing with this type of issue.

For more information on the forms cache and how to troubleshoot it see

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