To fix the issue you have to edit some auto-generated VSTO code and release the OutlookItem during a setup event like so:

private void RegionFactory_FormRegionInitializing(object sender, Outlook.FormRegionInitializingEventArgs e)
{
    Marshal.ReleaseComObject(e.OutlookItem);
}

This block of code can be found in the region block labeled: #region Form Region Factory

Apparently, a Microsoft support engineer posted about this back in August of 2008, but I never came across it until after working with a different very nice MSDN support engineer.

The other day however, I realized that the trick above does not in fact work for Distribution List (IPM.DistList) form regions. Watch the following video for proof!

I contacted the very nice engineer who helped me before to re-open/create a support ticket about the issue. While waiting for a response however, I kept trying to fix the issue and finally did. I’m quite hopeful that my fix is not the best answer, as it’s truly a bizarre hack.

Take a look at the Designer code generated for your region. The IFormRegionFactory which creates an instance of the actual ImportedFormRegion does not need to return anything for the region to load. In fact, if you throw an exception from IFormRegionFactory.CreateFormRegion, the DistListItem is properly unreferenced when the inspector is closed.

You can watch the following video to see it in action!

As you can see this isn’t very fancy – two check-boxes to control if you want the email and/or fax addresses sent along to PSES. Naturally, there is also an option to opt-in distribution lists:

This is of course where the fun began. In my personal opinion distribution lists were not properly implemented, or rather updated from earlier versions of Outlook. For instance, take a close look at the image above. Notice how a “fax” address is listed under the “E-mail” column? Do you also notice how it has the @ symbol? What in the world is going on here?

Another issue is how the ContactItem relates to the Recipient – or rather how you can obtain the actual contact from the item in the distribution list. Based on documentation we should be able to use the GetContact() method found a little ways down on the Recipient class.

Outlook.Recipient.AddressEntry.GetContact()

Sadly however, this doesn’t work (for me at-least) no matter what I did. So after a decent amount of trial and error I was able to determine that a Recipient’s EntryID actually contains the the Contact’s EntryID.

For example:

Recipient.EntryID = "abcd-1234";
Contact.EntryID = "1234";

This is simplified of course as real ID’s are quite long. So to actually get the contact we should do this:

Outlook.Recipient r = DistListItem.GetMember(1);
string rid = r.EntryID;
rid = rid.Substring(rid.Length - 48);

Outlook.ContactItem c = Application.Session.GetItemFromID(rid, null) as Outlook.ContactItem;

Hopefully someone else will find this mess useful as I couldn’t find anything a year ago about these oddities and issues.