Behavior changes in Outlook : MAPI & Custom properties

  • Article

Per the knowledgebase the implementation of MAPI in Outlook has been changed to control how custom properties can be created. To guarantee consistent use of custom properties, custom properties must already be used in the organization or on the Outlook client. As soon as custom properties are being used or are registered, the custom properties can be freely transmitted to other Outlook clients or to servers that are running Exchange Server. The custom properties can also be sent over the Internet.

E-mail messages are typically sent in MIME format over the Internet. When Outlook receives an Internet e-mail message, the message is converted into a MAPI representation. The following are examples of Internet e-mail protocols:

  • POP
  • IMAP
  • HTTP (Hotmail)

By default, Outlook no longer enables Internet mail to create new custom properties. Only properties that are already created in the default mail delivery store are preserved for incoming e-mail messages.

This change mostly affects messages that are sent in encapsulated TNEF (Winmail.dat), where the sender has used the Send using Outlook Rich Text Format option. However, Internet messages that contain X-message header properties are also affected.
Note Messages that contain custom properties that are sent in an Exchange organization are not affected by these changes.

Custom properties can also be saved in .msg files and in .oft files. If a user opens a .msg file that has custom properties, those custom properties are not saved to the default store when the message is saved, forwarded, and so on. Typically, .oft files are used to back up Outlook custom forms. With .oft files, the new behavior applies to all kinds of items. The custom form will not open. Instead, the message will appear in the default form for that particular item type.

In summary, this change in design can cause two things to occur:

  • Outlook ignores non-existing custom properties. If a custom property does not exist in the delivery store, the property will not be created, and its value will be lost. If the custom property already exists in the delivery store, its value is persisted. This change applies to the following:
    • Internet e-mail messages that have TNEF and their embedded messages.
    • S/MIME messages.
    • .msg files when you drop the .msg file into an Outlook item window to add the file to another item. This change also applies to .msg files when you drop the .msg file into the main Outlook window to add the file to a folder or in the Microsoft Word window when you use Word as the e-mail editor.
    • .msg files that a user double-clicks or right-clicks to open.
  • Outlook ignores the one-off form definition. If a one-off form specifies a custom property and that custom property does not exist in the delivery store, the one-off form is not rendered. Instead, the user will see the default form for that particular item type. This change applies to Internet e-mail messages that contain a one-off form definition that is encapsulated in TNEF. This change also applies to .oft files that a user double-clicks or right-clicks to open.