CDO.Message

function mail(from,to,subject,text) {
    var cdoMsg = new ActiveXObject("CDO.Message");
    var cdoCfg = new ActiveXObject("CDO.Configuration");
    cdoCfg.fields("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2; // cdoSendUsingPort
    cdoCfg.fields("http://schemas.microsoft.com/cdo/configuration/smtpserver") = "smtp.yandex.ru";
    cdoCfg.fields("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = 25;
    cdoCfg.fields("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate") = 1; // cdoBasic
    cdoCfg.fields("http://schemas.microsoft.com/cdo/configuration/sendusername") = "sender@promo.ru";
    cdoCfg.fields("http://schemas.microsoft.com/cdo/configuration/sendpassword") = "sender";
    cdoCfg.fields.Update();
    cdoMsg.Configuration = cdoCfg;
    cdoMsg.BodyPart.Charset = "windows-1251";
    cdoMsg.From      = from;
    cdoMsg.To        = to;
    cdoMsg.Subject   = subject;
    cdoMsg.TextBody  = text;
    cdoMsg.send();
}

mail("test@promo.ru", "sender@promo.ru", "Это тест", "Это тестовое письмо CDO - кодировка в порядке?");