function emailCheck (emailStr) {
              /* The following variable tells the rest of the function whether or not
              to verify that the address ends in a two-letter country or well-known
              TLD.  1 means check it, 0 means don't. */
var checkTLD=1;
              /* The following is the list of known TLDs that an e-mail address must end with. */
var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum)$/;
              /* The following pattern is used to check if the entered e-mail address
              fits the user@domain format.  It also is used to separate the username
              from the domain. */
var emailPat=/^(.+)@(.+)$/;
              /* The following string represents the pattern for matching all special
              characters.  We don't want to allow special characters in the address. 
              These characters include ( ) < > @ , ; : \ " . [ ] */
var specialChars="\\(\\)><@,;:\\\\\\\"\\.\\[\\]";
              /* The following string represents the range of characters allowed in a 
              username or domainname.  It really states which chars aren't allowed.*/
var validChars="\[^\\s" + specialChars + "\]";
              /* The following pattern applies if the "user" is a quoted string (in
              which case, there are no rules about which characters are allowed
              and which aren't; anything goes).  E.g. "jiminy cricket"@disney.com
              is a legal e-mail address. */
var quotedUser="(\"[^\"]*\")";
              /* The following pattern applies for domains that are IP addresses,
              rather than symbolic names.  E.g. joe@[123.124.233.4] is a legal
              e-mail address. NOTE: The square brackets are required. */
var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;
              /* The following string represents an atom (basically a series of non-special characters.) */
var atom=validChars + '+';
              /* The following string represents one word in the typical username.
              For example, in john.doe@somewhere.com, john and doe are words.
              Basically, a word is either an atom or quoted string. */
var word="(" + atom + "|" + quotedUser + ")";
              // The following pattern describes the structure of the user
var userPat=new RegExp("^" + word + "(\\." + word + ")*$");
              /* The following pattern describes the structure of a normal symbolic
              domain, as opposed to ipDomainPat, shown above. */
var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$");
              /* Finally, let's start trying to figure out if the supplied address is valid. */
              /* Begin with the coarse pattern to simply break up user@domain into
              different pieces that are easy to analyze. */
var matchArray=emailStr.match(emailPat);
if (matchArray==null) {
              /* Too many/few @'s or something; basically, this address doesn't
              even fit the general mould of a valid e-mail address. */
  alert("Email address seems incorrect -- check @'s and .'s");
  return false;
}
var user=matchArray[1];
var domain=matchArray[2];
              // Start by checking that only basic ASCII characters are in the strings (0-127).
for (i=0; i<user.length; i++) {
  if (user.charCodeAt(i)>127) {
    alert("Ths username contains invalid characters.");
    return false;
  }
}
for (i=0; i<domain.length; i++) {
  if (domain.charCodeAt(i)>127) {
    alert("This domain name contains invalid characters.");
    return false;
  }
}
              // See if "user" is valid 
if (user.match(userPat)==null) {
              // user is not valid
  alert("Sorry, your email username doesn't seem to be valid.");
  return false;
}
              /* if the e-mail address is at an IP address (as opposed to a symbolic
              host name) make sure the IP address is valid. */
var IPArray=domain.match(ipDomainPat);
if (IPArray!=null) {
              // this is an IP address
for (var i=1;i<=4;i++) {
  if (IPArray[i]>255) {
    alert("Destination IP address is invalid!");
    return false;
  }
}
return true;
}
              // Domain is symbolic name.  Check if it's valid.
var atomPat=new RegExp("^" + atom + "$");
var domArr=domain.split(".");
var len=domArr.length;
for (i=0;i<len;i++) {
  if (domArr[i].search(atomPat)==-1) {
    alert("Sorry, your email 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 -- com, org, gov, etc. -- 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;
}