// JavaScript Document
<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->
function emailCheck (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) {
	return "The e-mail address seems to be incorrect. Please check the @ and .'s"
}
var user=matchArray[1]
var domain=matchArray[2]
if (user.match(userPat)==null) {
    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 "The IP address, which appears after the @ sign is invalid"
	    }
    }
    return true
}
var domainArray=domain.match(domainPat)
if (domainArray==null) {
    return "The domain name does not seem to be valid"
}
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) {
   return "The e-mail address must end in a valid domain, e.g .com or .co.uk"
}
if (len<2) {
   var errStr="The e-mail address is missing a hostname"
   return errStr
}

return '';
}