The Outlook 2010 MAPI Reference has been updated. I don’t have a list of everything that changed, so I’ll highlight one addition that’s pretty cool: the property definition stream. Long time readers might remember I mentioned this property before – it’s one of the properties you want to delete to kill a one-off form. It’s also the property that Outlook uses to store information about named properties created via the Object model and the user interface.

Now that the format of PidLidPropertyDefinitionStream is documented, you can create new user defined properties using MAPI and have them show up in the UI! The September release of MFCMAPI (which I’m furiously hammering on) will be able to parse this property.

As usual, the documentation is also available for download.