我如何知道用户何时阅读重要的电子邮件通知？

Our company frequently issues important notices via e-mail as do many other companies do I'm sure. Our management team has turned to us to see if there is any way of knowing when a user reads this important information. I realize forcing a read receipt via e-mail is not reliable at all, so we are trying to explore other options available to us.Our company frequently issues important notices