This article assumes that it is possible to determine if the mail has been read. For the methods to do this see https://en.wikipedia.org/wiki/Email_tracking htt

This article assumes that it is possible to determine if the mail has been read. For the methods to do this see https://en.wikipedia.org/wiki/Email_tracking https://en.wikipedia.org/wiki/Email_tracking. For a real plain-text email you can only use Read-Receipts but several mail readers don't support this and even for those that support it the default setting is probably "Off". That leaves only the creepy use of tracking images (e.g. the famous single pixel gif), and most privacy conscious users will not load these images.