private void linkLabel1_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
{
    System.Diagnostics.Process.Start("mailto:amysimple@qq.com");
}

[System.Runtime.InteropServices.DllImport("shell32.dll", EntryPoint = "ShellExecuteA")]
public static extern int ShellExecute(
    int hwnd,
    String lpOperation,
    String lpFile,
    String lpParameters,
    String lpDirectory,
    int nShowCmd
);

private void linkLabel2_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
{
    ShellExecute(0, String.Empty, "mailto:amysimple@qq.com", String.Empty, String.Empty, 1);
}