function _onClickWriteEmail() {
            // Get project names from labels in #selected-projects div.
            var sMailingType = $('[name=mailingType]:checked').val();
            var waProjectSpan, aProjects;
            if (sMailingType == 'all') {
                aProjects = {'all': 'true'}
            } else {
                waProjectSpan = $('#selected-projects > .label');
                aProjects = [];
                for (var i = 0; i < waProjectSpan.length; i++) {
                    aProjects.push(waProjectSpan[i].childNodes[0].nodeValue.trim());
                }
            }

            // Send a request contains project names to get email addresses and
            // launch user's mail client with them using mailto scheme.
            htElement.welBtnWriteEmail.button('loading');

            $yobi.sendForm({
                "sURL"      : htVar.sURLMailList,
                "htOptForm": {"method":"POST"},
                "htData"    : aProjects,
                "sDataType" : "json",
                "fOnLoad"   : function(data) {
                    var form = $('<form>');
                    var mailto = 'mailto:';
                    for (var i = 0; i < data.length; i++) {
                        mailto += data[i] + ',';
                    }
                    console.log(mailto);
                    form.attr('method', 'POST');
                    form.attr('action', mailto);
                    form.attr('enctype', 'text/plain');
                    form.submit();
                    htElement.welBtnWriteEmail.button('reset');
                }
            });
        }
Launch a mail client to write an email.