发邮件？？？？？？？

[flysky2006]

private void Button1_Click(object sender, System.EventArgs e)
{
if(Page.IsValid==true)
{
string to2,from2,cc2,bcc2,topic2,content2;
to2=to.Text;
from2=from.Text;
cc2=cc.Text;
bcc2=bcc.Text;
topic2=topic.Text;
content2=content.Text;
MailMessage mm=new MailMessage();
mm.From=from2.ToString();
mm.To=to2.ToString();
mm.Cc=cc2.ToString();
mm.Bcc=bcc2.ToString();
mm.Subject="topic2";
mm.Priority=MailPriority.High;
mm.BodyEncoding=System.Text.Encoding.GetEncoding("Gb2312");

mm.BodyFormat=(MailFormat)bodyformail.SelectedIndex;
mm.BodyFormat=MailFormat.Html;
mm.Body="content2";

try
{
SmtpMail.SmtpServer="smtp.sina.com.cn";//设置SMTP服务
SmtpMail.Send(mm);
Label1.Text="发送成功!";
}
catch(Exception ex)
{
Label1.Text=ex.ToString();
}
}

}

[flysky2006]

System.Web.HttpException: 未能访问“CDO.Message”对象。 ---> System.Reflection.TargetInvocationException: 调用的目标发生了异常。 ---> System.Runtime.InteropServices.COMException (0x8004020F): 服务器拒绝了一个或多个收件人地址。服务器响应为: 554 : Client host rejected: Access denied --- 内部异常堆栈跟踪的结尾 --- at System.RuntimeType.InvokeDispMethod(String name, BindingFlags invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers, Int32 culture, String[] namedParameters) at System.RuntimeType.InvokeMember(String name, BindingFlags invokeAttr, Binder binder, Object target, Object[] args, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParameters) at System.Web.Mail.LateBoundAccessHelper.CallMethod(Object obj, String methodName, Object[] args) --- 内部异常堆栈跟踪的结尾 --- at System.Web.Mail.LateBoundAccessHelper.CallMethod(Object obj, String methodName, Object[] args) at System.Web.Mail.CdoSysHelper.Send(MailMessage message) at System.Web.Mail.CdoSysHelper.Send(String from, String to, String subject, String messageText) at System.Web.Mail.SmtpMail.Send(String from, String to, String subject, String messageText) at WebA2.WebForm1.Button2_Click(Object sender, EventArgs e) in d:\inetpub\wwwroot\weba2\webform1.aspx.cs:line 112

[flysky2006]

以上是发送代码和提示错误
那位高手可解？