function emailCheck (emailStr) {
  var checkTLD=1;
  var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum)$/;
  var emailPat=/^(.+)@(.+)$/;
  var specialChars="\\(\\)><@,;:\\\\\\\"\\.\\[\\]";
  var validChars="\[^\\s" + specialChars + "\]";
  var quotedUser="(\"[^\"]*\")";
  var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;
  var atom=validChars + '+';
  var word="(" + atom + "|" + quotedUser + ")";
  var userPat=new RegExp("^" + word + "(\\." + word + ")*$");
  var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$");
  var matchArray=emailStr.match(emailPat);
  if (matchArray==null) {
    alert("Email address seems incorrect (check @ and .'s)");
    return false;
  }
  var user=matchArray[1];
  var domain=matchArray[2];
  for (i=0; i<user.length; i++) {
    if (user.charCodeAt(i)>127) {
      alert("Ths username contains invalid characters.");
      return false;
    }
  }
  for (i=0; i<domain.length; i++) {
    if (domain.charCodeAt(i)>127) {
      alert("Ths domain name contains invalid characters.");
      return false;
    }
  }
  if (user.match(userPat)==null) {
    alert("The username doesn't seem to be valid.");
    return false;
  }
  var IPArray=domain.match(ipDomainPat);
  if (IPArray!=null) {
    for (var i=1;i<=4;i++) {
      if (IPArray[i]>255) {
        alert("Destination IP address is invalid!");
        return false;
      }
    }
    return true;
  }
  var atomPat=new RegExp("^" + atom + "$");
  var domArr=domain.split(".");
  var len=domArr.length;
  for (i=0;i<len;i++) {
    if (domArr[i].search(atomPat)==-1) {
      alert("The domain name does not seem to be valid.");
      return false;
    }
  }
  if (checkTLD && domArr[domArr.length-1].length!=2 && domArr[domArr.length-1].search(knownDomsPat)==-1) {
    alert("The address must end in a well-known domain or two letter " + "country.");
    return false;
  }
  if (len<2) {
    alert("This address is missing a hostname!");
    return false;
  }
  return true;
}