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namespace Newsletter
{
    class Email : Form1 
    {
        static void CreateSendItem(Microsoft.Office.Interop.Outlook.Application application)
        {
            Microsoft.Office.Interop.Outlook.Application oApp = new Microsoft.Office.Interop.Outlook.Application();
            Microsoft.Office.Interop.Outlook._NameSpace oNameSpace = oApp.GetNamespace("MAPI");
            oNameSpace.Logon(null, null, true, true);  //angemelden Nutzer benutzen
            Microsoft.Office.Interop.Outlook._MailItem oMailItem = (Microsoft.Office.Interop.Outlook._MailItem)oApp.CreateItem(Microsoft.Office.Interop.Outlook.OlItemType.olMailItem);
            oMailItem.To = "xx@xx.com";
            oMailItem.Subject = "test";
            oMailItem.Body = "bla";
            Microsoft.Office.Interop.Outlook.MAPIFolder oOutboxFolder = oNameSpace.GetDefaultFolder(Microsoft.Office.Interop.Outlook.OlDefaultFolders.olFolderOutbox);
            oMailItem.SaveSentMessageFolder = oOutboxFolder;
            //uncomment this to also save this in your draft    
            //oMailItem.Save(); 
            //adds it to the outbox      
            oMailItem.Send();
        }
    }
}                    

1:

Email.CreateSendItem(YourOutlookApplication)