问题
I need to track if the email generated by the system is read by the user. For this, I am currently adding an img of 1x1 gif to the email content with src pointing to my hosted web application. In the web application, I have added a servlet filter to track all GET requests.
This is working, but for some clients the image is not automatically downloaded, hence I am not able to track the request. Any other alternative/better suggestions? I have seen Ireadit and Spypig. It's not feasible to use them.
回答1:
No, there is no fool-proof way of detecting if an email has been read. As you've found, privacy and security restrictions in all the major email clients exist in part to prevent what you're doing.
回答2:
Even in the year 2016 there are many people who probably do not like the idea of such things going on in the background.
And many email clients simply refuse "downloading images" by default. In that case you still depend on the user clicking "download images" somehow.
So the short answer is: you will have to live with such restrictions of this process. The mail protocol doesn't allow for "has been read checks"; and anything you do to circumvent that ... will stay a circumvention.
And my personal two cent: even when that image gets uploaded, that doesn't really tell you that the mail was read. It can still happen that your users open the mail in some preview area and just delete it half a second later. Or some kind of automation (like anti-virus) triggers the download.
来源：https://stackoverflow.com/questions/41145347/track-if-the-email-is-read-by-the-client