//<script>

function emailCheck (emailStr) { 

  if (emailStr == '') return true; 

  /* 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 "Email address seems incorrect (check @ and .'s)" 
  } 
  var user=matchArray[1] 
  var domain=matchArray[2] 

  // See if "user" is valid 
  if (user.match(userPat)==null) { 
      // user is not valid 
      return "The username doesn't seem to be valid."; 
  } 

  /* 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 "Destination IP address is invalid!" 
       } 
      } 
      return "" 
  } 

  // Domain is symbolic name 
  var domainArray=domain.match(domainPat) 
  if (domainArray==null) { 
   return "The domain name doesn't seem to be valid."; 
  } 

  /* 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 "The address must end in a three-letter domain, or two letter country."; 
  } 

  // Make sure there's a host name preceding the domain. 
  if (len<2) { 
     var errStr="This address is missing a hostname!" 
     return errStr; 
  } 

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