var emailRegExp = /^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$/g;

function echeck(field) {
	var str = field.value;
	if (emailRegExp.test(str))
	{
    		return true;
	}
	else
	{
		alert("Please enter a valid email address");
		field.focus();
		return false;
	}
}