function checkemail(name, data, allowednull)
{
  var datastr = data;
  var lefttrim = datastr.search(/\S/gi);
  
  if (lefttrim == -1) {
    if (allowednull) {
      return 1;
    } else {
      alert("请输入一个正确的E-mail地址！");
      return -1;
    }
  }
  var myRegExp = /[a-z0-9](([a-z0-9]|[_\-\.][a-z0-9])*)@([a-z0-9]([a-z0-9]|[_\-][a-z0-9])*)((\.[a-z0-9]([a-z0-9]|[_\-][a-z0-9])*)*)/gi;
  var answerind = datastr.search(myRegExp);
  var answerarr = datastr.match(myRegExp);
  
  if (answerind == 0 && answerarr[0].length == datastr.length)
  {
    return 0;
  }
  
  alert("请输入一个正确的E-mail地址！");
  return -1;
}