I have a software that sends notifications, quotes and invoices to "clients of my clients" by email. Sometimes people don't answer it very fast, so someone needs to call by phone to confirm if they received and get the feedback. I would like to automate this, to know if them, at least, read the email. I know this is very difficult due to how email works, but some companies already try to do this in a satisfactory way, like:
In HTML mail messages we can create a resource that points to the server, like a image. But mail clients usually ask permission to the user to load the images. So, problem here.
But for text mail messages? Is there any way to know the email was read? How companies these companies do?
PS: I don't know what tags is the best to classify my answer, I shall appreciate any edit.
There is no way to be 100% sure if a email was opened, because of its architecture. There are some techniques to do this, but it always depends of user actions and mail client configurations. But:
About opening tracking:
Opens are tracked by including a transparent .png file, which will only work if there is an HTML component to the email (i.e., text only emails will not track opens). You should note that many email service providers disable images by default, so this data will only show up if the recipient clicks on display images button in his/her email.
(Text extracted from mailgun.com user docs)
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