function checkemail(emailStr) {
	var testresults;
	//var str=document.validation.emailcheck.value
	var filter=/^([\w-]+(?:\.[\w-]+)*)@((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$/i

	if (filter.test(emailStr)) {
		testresults = true;
	} else {
		//alert("Please input a valid email address!")
		testresults = false;
	}
	
	return (testresults);
}


<!-- V1.1.3: Sandeep V. Tamhankar (stamhankar@hotmail.com) -->
function emailCheck (emailStr) {
var checkTLD=1;
var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum)$/i;
var emailPat=/^(.+)@(.+)$/;
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 userPat=new RegExp("/^" + word + "(\\." + word + ")$/");
//var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$",['i']);
var domainPat=new RegExp("/^" + atom + "(\\." + atom +")$/",['i']);

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];
alert("user == " + user);
alert("doman == " + domain);
for (i=0; i<user.length; i++) 
	{
	if (user.charCodeAt(i)>127) 
		{
		alert("Ths username part of the email address contains invalid characters.");
		return false;
   		}
	}
for (i=0; i<domain.length; i++) 
	{
	if (domain.charCodeAt(i)>127) 
		{
		alert("Ths domain name in the email address contains invalid characters.");
		return false;
   		}
	}

if (user.match(userPat)==null) 
	{
	alert("The username part of 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 atomPat=new RegExp("^" + atom + "$");
var domArr=domain.split(".");
var len=domArr.length;
for (i=0;i<len;i++) 
	{
	if (domArr[i].search(atomPat)==-1) 
		{
		alert("The domain name in the email address does not seem to be valid.");
		return false;
   		}
	}

if (checkTLD && domArr[domArr.length-1].length!=2 && 
	domArr[domArr.length-1].search(knownDomsPat)==-1) 
	{
	alert("The address must end in a well-known domain or two letter country.");
	return false;
	}


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

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