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];

  // Start by checking that only basic ASCII characters are in the strings (0-127).

  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;
     }
  }

  // See if "user" is valid 

  if (user.match(userPat)==null) {

  // user is not valid

  alert("The username doesn't seem to be valid.");
  return false;
  }

  /* if the e-mail address is at an IP address (as opposed to a symbolic
  host name) make sure the IP address is valid. */

  var IPArray=domain.match(ipDomainPat);
  if (IPArray!=null) {

  // this is an IP address

  for (var i=1;i<=4;i++) {
  if (IPArray[i]>255) {
  alert("Destination IP address is invalid!");
  return false;
     }
  }
  return true;
  }

  // Domain is symbolic name.  Check if it's valid.
 
  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;
     }
  }

  /* domain name seems valid, but now make sure that it ends in a
  known top-level domain (like com, edu, gov) or a two-letter word,
  representing country (uk, nl), and that there's a hostname preceding 
  the domain or country. */
  
  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;
  }

  // Make sure there's a host name preceding the domain.

  if (len<2) {
  alert("This address is missing a hostname!");
  return false;
  }

  // If we've gotten this far, everything's valid!
  return true;
}