无法通过App引擎发送SMTP电子邮件

I have created a go application that sends an email using net/smtp and PlainAuth. And everything is working fine. But when I deploy this same code on the google app engine it is not sending. If I serve using goapp serve it work locally. Below is the code:

func sendMail(body string, subject string) {
var err error
var doc bytes.Buffer
auth := smtp.PlainAuth("",
    "from@gmail.com",
    "********",
    "smtp.gmail.com")

parameters := &SmtpTemplateData{
    "from@gmail.com",
    "to@gmail.com",
    "Subject",
body,
}

buffer := new(bytes.Buffer)

template := template.Must(template.New("emailTemplate").Parse(emailScript()))
template.Execute(buffer, parameters)

t := template.New("emailTemplate1")
t, err = t.Parse(emailTemplate)
if err != nil {
    fmt.Println("error trying to parse mail template")
}
err = t.Execute(&doc, parameters)


smtp.SendMail(
        "smtp.gmail.com:587",
        auth,
        "from@gmail.com",
        []string{"to@gmail.com"},
        doc.Bytes(),
)
}