function checkEmail (emailStr) {
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]

if (user.match(userPat)==null) {
   alert("The email address doesn't seem to be valid.")
   return false
}

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

var domainArray=domain.match(domainPat)
if (domainArray==null) {
       alert("The domain name doesn't seem to be valid.")
   return false
}

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) {
  alert("The address must end in a three-letter domain, or two letter country.");
  return false;
}

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

return true;
}