private void textBox1_Validated(object sender,EventArgs e)
  {
   errorProvider1.SetError(this.textBox1,"");
  }

  public bool ValidEmailAddress(string emailAddress,out string errorMessage)
  {
   //首先判断是否为空，然后判断是否有@,.符号
   if(emailAddress.Length==0)
   {
    errorMessage="e-mail address is required.";
    return false;
   }
   //是否包含@
   if(emailAddress.IndexOf("@")>-1)
   {
    //从@往后面开始搜索，找到.的位置，如果位置大于@的位置说明格式正确
    if(emailAddress.IndexOf(".",emailAddress.IndexOf("@"))>emailAddress.IndexOf("@"))
    {
     errorMessage="";
     return true;
    }
   }

   errorMessage="e-mail address must be valid e-mail address format.\n"+"For example 'someone@example.com'";
   return false;
  }

  /// <summary>
  /// 清理所有正在使用的资源。
  /// </summary>
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }

  #region Windows 窗体设计器生成的代码
  /// <summary>
  /// 设计器支持所需的方法 - 不要使用代码编辑器修改
  /// 此方法的内容。
  /// </summary>
  private void InitializeComponent()
  {
   this.textBox1 = new System.Windows.Forms.TextBox();
   this.errorProvider1 = new System.Windows.Forms.ErrorProvider();
   this.SuspendLayout();
   //
   // textBox1
   //
   this.textBox1.Location = new System.Drawing.Point(72, 88);
   this.textBox1.Name = "textBox1";
   this.textBox1.TabIndex = 0;
   this.textBox1.Text = "";
   //
   // errorProvider1
   //
   this.errorProvider1.ContainerControl = this;
   //
   // Form1
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
   this.ClientSize = new System.Drawing.Size(292, 273);
   this.Controls.Add(this.textBox1);
   this.Name = "Form1";
   this.Text = "Form1";
   this.ResumeLayout(false);