At least one mailng list checked

At the moment you can add a validation check writing some javascript and include it in your theme footer.php (remind also to enquque jQuery in your theme):

<script type="text/javascript">
    jQuery(document).ready( function($) {
        $('.alo_easymail_widget_form').on('submit', function(e) {
			if( $('.alo_easymail_lists_table input [type=checkbox]:checked').length > 0 ) {
				// ok, submit
			} else {
				e.preventDefault();
				$('#alo_easymail_widget_feedback').addClass('alo_easymail_widget_error').html('Please select one or more lists').show();
				return false;
			}
		} );
    });
</script>

I’ve not tested a lot, but I think it can be a good starting point for you.

Thanks. Altough something else is submiting that form whenever an e-mail is valid. There is onsubmit=”alo_em_pubblic_form();return false;” attribute on form tag. Is there a way to fire that function after checking if at least one list was selected?