CDO not sending internal mails

I am using CDO from sending emails. It is the only way I found that works from a certian customer. Standard smtp sending does not

the problem with this method is that it works ok for external email recipients but not for the internal ones.

    CDO.Message oMsg = new CDO.Message();
    CDO.IConfiguration iConfg;
    iConfg = oMsg.Configuration;
    ADODB.Fields oFields;
    oFields = iConfg.Fields;
    ADODB.Field oField = oFields["http://schemas.microsoft.com/cdo/configuration/sendusing"];
    oField.Value = 2;
    ADODB.Field oServer = oFields["http://schemas.microsoft.com/cdo/configuration/smtpserver"];
    oServer.Value = Server;

    oFields.Update();
    oMsg.Subject = subject;
    oMsg.From = Sender;
    oMsg.To = recipient;
    oMsg.HTMLBody = body;
    oMsg.Send();

Hope someone has an idea The code does not break it just does not send an emal.

Can I get an error from the object somehow?