各位老师麻烦帮我看一下，以下自动登录邮箱代码

[sgyxslscxh]

public void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{

HtmlElement tbUserid = webBrowser1.Document.All["username"]; //获取用户名对应元素
HtmlElement tbPasswd = webBrowser1.Document.All["password"]; //获取密码对应元素
if (tbUserid == null || tbPasswd == null)
return;
tbUserid.SetAttribute("value", "[e-mail]"); //给用户名赋值
tbPasswd.SetAttribute("value", "mima"); //给密码赋值
}

private void button1_Click(object sender, EventArgs e)
{
HtmlElement btnSubmit = webBrowser1.Document.All["loginBtn"]; //获取登录对应元素
btnSubmit.InvokeMember("click"); //模拟点击登录按钮
}

代码不能重新设置邮箱名，怎样解决？