Outlook.Application.CreateItem with Office365 says: The operation failed - outlook

Question

We've written an Outlook plugin using Add-in-Express. Code:
private void CreateShowMessageUsingCreateItem(Outlook._Application OutlookApp)
{
Outlook.MailItem mail = null;
try
{
mail = OutlookApp.CreateItem(Outlook.OlItemType.olMailItem) as Outlook.MailItem;
mail.Save();
mail.Display(false);
}
catch (Exception ex)
{
System.Windows.Forms.MessageBox.Show(ex.Message);
}
finally
{
if (mail != null) Marshal.ReleaseComObject(mail);
}
}
Works when Outlook is connected to Exchange. Fails when
Outlook is connected to Office365. Error:
Exception: System.Runtime.InteropServices.COMException (0x80004005): The operation failed.
at Microsoft.Office.Interop.Outlook.ApplicationClass.CreateItem(OlItemType ItemType)
at DocuSignInk.DSToolbox.ShowResponse(MailItem senderEmail) in C:\docusign_source\Ink_Outlook\DocuSignInk\DSToolbox.cs:line 540
Some research indicates that you need to release your objects
when making these calls in a loop. But I'm not in a loop. I
can't even get one call to work, so I don't get to the point
where I can release anything.
Testing with Wireshark and Charles indicates that the problem is
in the client. I was trying to see if there is a more detailed
error coming from the server, but there's no traffic to the server
at all.
A quick Python script works from the command line.
import win32com.client
outlook = win32com.client.Dispatch('Outlook.Application')
mail = outlook.CreateItem(win32com.client.constants.olMailItem)
mail.Save()
mail.Display(False)
So it must be something in the client. I'm guessing maybe thread-related?

Answer 1

This can happen if you haven't activated Microsoft Office (which includes Outlook).
Short, test add-ins can work if they run right away before the activation check happens.
Once the activation check happens the API calls will fail.

Answer 2

Firstly, the code is correct, no additional releasing is required. The most obvious reason is that your Outlook, when connected to Exchange Online, cannot create a mail item. You can check this with the following VBA macro:
Public Sub CreateEmailItem()
Dim mail As Outlook.MailItem
Set mail = Application.CreateItem(olMailItem)
mail.Save
mail.Display (False)
Set mail = Nothing
End Sub
Regards,
Dmitry Kostochko (Add-in Express Team)

Answer 3

I had the same exception along with HResult that was -2147467259.
The direct reason was an outlook popup window informing about its trial version or an outlook closing process which is pending after you have closed previous activities in outlook including an email that was showed up by executing the above code (this process is indicated by a respective tray icon in the taskbar until it disappears).
You need to close the window first or wait for the tray icon to disappear before you execute creating new email.