刚开始要建立一个发送邮件的页面，但碰到问题了：
import namespace="system.web.mail"

Sub btnSubmit_Click(sender As Object, e As EventArgs)
dim ML as mailMessage=New mailMessage()
ML.to=Ctype(viewstate("email_to"),string)
ML.from="xxx@yyy.com"
ML.subject=txtSubject.text
ML.body=txtEnquiry.text

ML.fields.add("http://schemas.microsoft.com/cdo/confiuration/smtpauthenticate","1")
ML.fields.add("http://schemas.microsoft.com/cdo/configuration/sendusername","xxx@yyy.com")
ML.fields.add("http://schemas.microsoft.com/cdo/configuration/sendpassword","aaaaa")

smtpMail.smtpServer="mail.yyy.com"
smtpMail.send(ML)
end sub

验证的设置没有错，请帮我看看哪里出问题了。可是为什么提示：

The server rejected the sender address. The server response was: 553 <xxx@yyy.com>: Sender address rejected: not logged in