function emailCheck(emailStr) {
  /* 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. */
    return 1;
  }

  var user   = matchArray[1];
  var domain = matchArray[2];

  // See if "user" is valid 
  if (user.match(userPat) == null) {
    // user is not valid
    return 2;
  }

  /* 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) {
        return 3;
      }
    }
  }

  // Domain is symbolic name
  var domainArray = domain.match(domainPat);

  if (domainArray == null) {
    return 4;
  }

  /* domain name seems valid, but now make sure that it ends in a
     three-letter word (like com, edu, gov) or a two-letter word,
     representing country (uk, nl), and that there's a hostname preceding 
     the domain or country. */
  /* Now we need to break up the domain to get a count of how many atoms
     it consists of. */
  var atomPat = new RegExp(atom, "g");
  var domArr  = domain.match(atomPat);
  var len     = domArr.length;

  if (domArr[domArr.length - 1].length < 2 || domArr[domArr.length - 1].length > 3) {
    // the address must end in a two letter or three letter word.
    return 5;
  }

  // Make sure there's a host name preceding the domain.
  if (len < 2) {
    return 6;
  }

  return 7;
  // If we've gotten this far, everything's valid!
}