Email raid receipts

No, there is not. There is the sneaky system used by spammers as well as "legitimate" senders that embed a link in an HTML-formatted message to an external image, often just one invisible pixel. Retrieving this image, sometimes called a "web beacon" will alert a monitoring server somewhere that can tell the sender that the recipient has opened the email... *IF* the recipient is set up to automatically display external images. The average sender wouldn't usually have a way to monitor this - it requires access to a web server. Thunderbird (and virtually all other) email clients have a setting to disable auto image display, and I would encourage everyone to do so. You can enable auto-download for trusted senders if you want, but I would still discourage it. Safer to do it manually. In other words, yes, there is at least that method, but it's easily defeated, which pretty much makes it uselessly unreliable.