ExtJs 分页问题，看不到数据，在线等

Question

    在利用ExtJs4.2进行分页时，能够从后台获取到Json数据，但在Grid中只能看到有一条记录，而且是空的，帮忙看下为什么分页不成功   
        //数据部分
            var maillist = Ext.create('Ext.data.Store', {
                buffered: false,
                autoLoad: true,
                fields: ['SenderTrueName',
                        { name: 'SendDate', type: 'date', dateFormat: 'timestamp' },
                         'Title', 'Status', 'Id', 'Checked'],
                proxy: {
                    waitTitle: '提示',
                    waitMsg: '正在载入邮件数据...',
                    type: 'ajax',
                    url: '/Data/getMailList?UserId=' + UserId + '&Flag=' + Flag
                },
                reader: { 
                     type: 'json', 
                     totalProperty: 'Total',
                     root: 'mails' },
                     pageSize: 18
            });            //表格部分
            var mailtable = Ext.create('Ext.grid.Panel', {
                width: Ext.innerWidth,
                height: Ext.innerHeigh,
                forceFit: true,
                autoScroll: true,
                buffered: true,
                store: maillist,
                columns: [
            { xtype: 'rownumberer', header: '', width: 30 },
            { xtype: 'checkcolumn', header: '', width: 30, dataIndex: 'Checked' },
            { header: '发件人', dataIndex: 'SenderTrueName', width: 100 },
            { header: '邮件主题', dataIndex: 'Title', width: 300 },
            { header: '发件时间', dataIndex: 'SendDate', width: 120 },
            { header: '附件数量', dataIndex: 'AttachCount', width: 55 },
            { header: '状态', dataIndex: 'Status', width: 45 },
            { header: 'id', dataIndex: 'Id', width: 20, hidden: true }
            ],
                selModel: new Ext.selection.Model({ mode: 'SIMPLE' }),
                //分页工具栏
                bbar: [{ 
                         xtype: 'pagingtoolbar', 
                         pageSize: 18, 
                         store: maillist, 
                         displayInfo: true, 
                         displayMsg: '第 {0} 页/共{1}邮件 邮箱中总计邮件{2}封 '}],
                listeners: {
                    //邮件表格事件
                }
            });      //后台返回的数据
   ｛ Total:266,mails:[{"SenderTrueName":"111","SendDate":"\/Date(1361525528000)\/","Status":"111","Title":"11","Id":6423327,"SenderId":"12593"},{"SenderTrueName":"1111","SendDate":"\/Date(1365919356000)\/","Status":"11","Title":"1111","Id":7176496,"SenderId":"44"}]｝Ext分页失败