function emailCheck(str) {

	var at="@";
	var dot=".";
	var lat=str.indexOf(at);
	var lstr=str.length;
	var ldot=str.indexOf(dot);
	var ok = "1234567890qwertyuiop[]asdfghjklzxcvbnm.@-_QWERTYUIOPASDFGHJKLZXCVBNM";

	if (str.indexOf(at)==-1){
		alert("Please enter a valid email address.");
		return false;
	}

	if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
		alert("Please enter a valid email address.");
		return false;
	}

	if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
		alert("Please enter a valid email address.");
		return false;
	}

	if (str.indexOf(at,(lat+1))!=-1){
		alert("Please enter a valid email address.");
		return false;
	}

	if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
		alert("Please enter a valid email address.");
		return false;
	}

	if (str.indexOf(dot,(lat+2))==-1){
		alert("Please enter a valid email address.");
		return false;
	}

	if (str.indexOf(" ")!=-1){
		alert("Please enter a valid email address.");
		return false;
	}
	 
	for(i=0; i < str.length ;i++){
		if(ok.indexOf(str.charAt(i))<0){ 
			alert('The email address contains invalid characters.');
			return false;
		}	
	} 

	return true;					
}