Email sent from C# OOM stays in Outbox if Outlook is closed until next Outlook start - vba

Question

I'm trying to send emails from a .NET application using Outlook Object Model.
My application displays the Outlook message window so the user can see what we're sending and edit it first. When the user hits the Send button, the Outlook window closes, and the message gets sent. This works perfectly as long as the Outlook application is already running.
If the Outlook application isn't already running, the message gets stuck in the Outbox, and will not send until I start Outlook. When I start Outlook, I can see the message sitting in the Outbox folder for a few seconds, then it gets sent.
I need to show the New Message form to Outlook user to select the recipient(s) and possibly edit the message before sending.
Note: I know that this question was already asked here Email sent with Outlook Object Model stays in Outbox until I start Outlook
and the solution exists, but it is not provided (only the small hint is provided) and unfortunately I cannot ask for clarification / code example because I have not enough "reputation".
I tried to write my own implementation of the hint provided, but the SyncEnd event is fired only when Outlook is already open (just to remind, the question is about the case then Outlook is closed).
My code below. What is wrong?
using Microsoft.Office.Interop.Outlook;
using OutlookApp = Microsoft.Office.Interop.Outlook.Application;
class Mailer
{
AutoResetEvent mailSentEvent = new AutoResetEvent(false);
public void CreateMail()
{
OutlookApp outlookApp = null;
MailItem mailItem = null;
try
{
outlookApp = new OutlookApp();
mailItem = outlookApp.CreateItem(OlItemType.olMailItem);
mailItem.Subject = "Test Message";
mailItem.Body = "This is the message.";
string reportPath = #"C:\temp\aaaaa.pdf";
mailItem.Attachments.Add(reportPath);
mailItem.Display(true);
StartSync(outlookApp);
bool result = mailSentEvent.WaitOne();
}
catch (System.Exception)
{
throw;
}
finally
{
if (mailItem != null) Marshal.ReleaseComObject(mailItem);
if (outlookApp != null) Marshal.ReleaseComObject(outlookApp);
}
}
private static SyncObject _syncObject = null;
private void StartSync(OutlookApp outlookApp)
{
var nameSpace = outlookApp.GetNamespace("MAPI");
_syncObject = nameSpace.SyncObjects[1];
_syncObject.SyncEnd += new Microsoft.Office.Interop.Outlook.SyncObjectEvents_SyncEndEventHandler(OnSyncEnd);
_syncObject.Start();
}
private void OnSyncEnd()
{
mailSentEvent.Set();
}
}

Answer 1

the SyncEnd event is fired only when Outlook is already open
That is not true. The SyncObjects collection contains all Send\Receive groups. You need to iterate over all objects in the collection and call the Start method, for example:
Set sycs = nsp.SyncObjects
For i = 1 To sycs.Count
Set syc = sycs.Item(i)
strPrompt = MsgBox("Do you wish to synchronize " &; syc.Name &;"?", vbYesNo)
If strPrompt = vbYes Then
syc.Start
End If
Next