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 +")*$");
  
  /* Begin with the coarse pattern to simply break up user@domain into
  different pieces that are easy to analyze. */
  
  var matchArray=emailStr.match(emailPat);
  if (matchArray==null) {
    return("Email address seems incorrect (check @ and .'s)");
  }
  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) {
      return("Ths username contains invalid characters.");
    }
  }
  
  for (i=0; i<domain.length; i++) {
    if (domain.charCodeAt(i)>127) {
      return("Ths domain name contains invalid characters.");
    }
  }
  
  // See if "user" is valid 
  
  if (user.match(userPat)==null) {
    // user is not valid
    return("The username doesn't seem to be valid.");
  }
  
  var IPArray=domain.match(ipDomainPat);
  if (IPArray!=null) {
    for (var i=1;i<=4;i++) {
      if (IPArray[i]>255) {
        return("Destination IP address is invalid!");
      }
    }
    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) {
      return("The domain name does not seem to be valid.");
    }
  }
  
  if (checkTLD && domArr[domArr.length-1].length!=2 && 
      domArr[domArr.length-1].search(knownDomsPat)==-1) {
    return("The address must end in a well-known domain or two letter " + "country.");
  }
  
  // Make sure there's a host name preceding the domain.
  if (len<2) {
    return("This address is missing a hostname!");
  }
  
  return("OK");

} // end function emailCheck()