How to stop email status tracking by senders who are using mailtrack.io or something similar?

Question

I found out, using "show original" on Gmail, that some business associates are embedding tracking into their sent emails (without any obvious warning/declaration), which tells them :

1. If I have received the email in my inbox
2. Number of times I have read it
3. Also sends them notifications when I read it (the worst part)

These people are not part of my company but with whom I have to interact closely over long periods of time.

I have already enabled "Do not show external images" but it does not work. I have explored Google forums but no article seems to address this exactly.

This is how it shows up in the "show original" option in Gmail:

What can I do to stop the received/unread/read status of my received emails from being tracked by the sender?

Edit 1: Ghostery claims it can block this (https://apps.ghostery.com/hu/apps/mailtrack.io), but I'd prefer a DIY approach, and I don't trust Ghostery with all the data it will get access to.

Edit 2: As asked in comment, browser used by me is Firefox (I've seen it working successfully even with Chrome). Only red flag in email privacy tester was for DNS pre-fetch. No other warning.

No helpful reply yet even on Google forums: https://productforums.google.com/forum/#!topic/gmail/3VJbpH1RdGk

Edit 3: This is another snippet from "show original" in Gmail, 0 pixel image I guess:

Maybe, Google is pinging the mailtrack server when I open the email (To download that "image" and show its own copy (thus generating a timestamp event)

Answer 1

If you don't want third party software like Ghostery or PixelBlock, one way to stop tracking via email is to disable automatic image loading in Gmail. The tracking is usually done via tiny images, so stopping these images from being loaded will prevent your data from being sent back to the tracker.

ITworld has instructions for how to disable automatic image loading:

https://www.itworld.com/article/2701379/consumerization/how-to-turn-off-automatic-image-loading-in-gmail.html

Answer 2

Send yourself an email from https://www.emailprivacytester.com/ and see what (if any) tracking vulnerabilities exist in your context (mail client, browser version, etc.)

Any single tracking vulnerability provides a vehicle for creating a time-stamped read receipt (and, depending on which vulnerability, potentially much more extensive information about your client).

Once the vulnerabilities are identified, you'll need to find browser settings (or a different client) that allow you to close ALL of the vulnerabilities.

In this particular case, you need to find a browser version and settings that will prevent DNS prefetch.

The emailprivacytester web site does note that:

Some mail servers do DNS lookups on these URLs as part of their spam filtering process, so you may see the IP address of the mail servers DNS resolvers here, as well as, or instead of, your own.

...so you may not be able to prevent it on a Gmail account if Google is in fact doing DNS lookups on the tracker link. But, if that's the case, it will only show the timestamp and IP of the Google server, and would not be a read receipt reflecting your behavior.