function gid (id)
{
    return document.getElementById(id);
}

function validMailAddress (mailAddress)
{
    var regExpMail = new RegExp("[A-Za-z0-9_]+([-+.][A-Za-z0-9_]+)*@[A-Za-z0-9_]+([-.][A-Za-z0-9_]+)*\\.[A-Za-z0-9_]{2,}([-.][A-Za-z0-9_]+)*");
    var result = regExpMail.exec(mailAddress);
    return (null == result) ? false : true;
}

function validMail ()
{
    if (false == validMailAddress(gid('mail-input').value)) {
        alert('Please enter e-mail');
        return false;
	} else {
		return true;
	}
}