作为一种解决方法，我们可以创建一个发送电子邮件"按钮以向用户发送电子邮件通知，如果您已完成任务的受让人设置，请单击按钮"以发送电子邮件.要发送电子邮件，我们可以使用REST API.

As a workaround, we can create a Send Email button to send an email notification to user, if you have finished set the Assignee of tasks, click the Button to send email. To send email we can use REST API.

通过SharePoint 2013中的REST API发送电子邮件通知

http://www.c- sharpcorner.com/article/send-email-notification-through-rest-api-in-sharepoint-2013/

或者我们可以创建一个工作流来发送电子邮件，使用呼叫Http Web服务"获取列表项数据并发送电子邮件，因为要发送邮件，我们需要使用持续时间暂停"操作等待几个小时.

Or we can create a workflow to send email, use Call Http Web Service to get the list items data and send email, as you want to send one, we need wait some hours using Pause for Duration action.

http://www. f***gwilliams.com/2013/09/04/创建一个sharepoint-timer-job-using-sharepoint-designer-2013/

***的问候，

丹尼斯