// returns error message string if invalid - returns "" if valid

function checkEmail(emailStr){
	emailPat=/^(.+)@(.+)$/
	specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]"
	validChars="\[^\\s" + specialChars + "\]"
	quotedUser="(\"[^\"]*\")"
	ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
	atom=validChars + '+'
	word="(" + atom + "|" + quotedUser + ")"
	userPat=new RegExp("^" + word + "(\\." + word + ")*$")
	domainPat=new RegExp("^" + atom + "(\\." + atom +")*$")
	matchArray=emailStr.match(emailPat)
	if (matchArray==null){
		return "Your e-mail address seems incorrect (check @ and .'s)";
	}
	user=matchArray[1]
	domain=matchArray[2]
	if (user.match(userPat)==null){
		return "The username doesn't seem to be valid.";
	}
	IPArray=domain.match(ipDomainPat)
	if (IPArray!=null){
		for (i=1;i<=4;i++){
			if (IPArray[i]>255){
				return "Destination IP address is invalid!";
			}
		}
	}
	domainArray=domain.match(domainPat)
	if (domainArray==null){
		return "Your domain name doesn't seem to be valid.";
	}
	atomPat=new RegExp(atom,"g");
	domArr=domain.match(atomPat);
	len=domArr.length;
	if (domArr[domArr.length-1].length<2 || domArr[domArr.length-1].length>4){
		return "Your e-mail address must end in a three or four-letter domain, or two letter country.";
	}
	if (len<2){
		return "Your address is missing a hostname!";
	}
	return "";
}