Understanding the forms cache
The forms cache is a folder located in the user's C:\Windows\…\Application Data\Forms folder that serves as a storage location for forms. The forms cache improves the load time of a form because commonly used forms are loaded from the hard disk rather than downloaded from the server. When a form is activated for the first time, the form definition file is copied from its forms library to the Forms folder. The forms cache keeps a temporary copy of the form definition in a subfolder whose name roughly matches the name of the form.
The form table, Frmcache.dat, also located in the Forms folder, is used to locate a form and to prevent multiple instances of the same form from being loaded in the cache. When a form is activated, Microsoft Outlook checks to see if a form with the same message class is already in the cache. If not, it copies the form definition to the cache. In addition, if a change has been made to a form, Outlook copies the new form definition to the cache.
Outlook looks for forms in the following order. When a match is found, Outlook opens the form and does not search further.
- Standard Outlook forms, such as Note, Post, and Contact, in the Application Forms Library
- Forms already cached in the form cache
- Forms published in the folder that’s currently selected
- Forms in the Personal Forms Library
- Forms in the Organizational Forms Library
Because Outlook caches forms, you should try to avoid having more than one form with the same name or publishing the same form to more than one forms library. Forms used in a folder-based solution should be published only in the folder. If you’re developing a solution based on mail message forms, you can temporarily publish the forms in your Personal Forms Library. Once the form is finalized, you should publish the form to the Organizational Forms Library on the Microsoft Exchange Server and delete the form from your Personal Forms Library after making a backup of the form. If, for some reason, you need to publish a form in more than one location, you should be sure to keep all forms libraries up-to-date with the current version of the form.
Note It is not possible to disable the forms cache. If you set the size of the form cache to 0, Outlook will not be able to open any custom forms.