Kyle Wiggers over at Digital Trends published a good round up of email tracking techniques deployed by most of the ad networks of the world. From the classic 1×1 magic pixel right through to deep cookie chaining analysis.
It was discovered that around 40% of your emails are being tracked for marketing purposes. That was a little higher than I would have thought, but this includes newsletters that you may be getting from the likes of Medium, Quora etc, as well as the typical daily/weekly emails from newspapers who rely heavily on the income from the adverts.
If you want to scrub all your email then consider using a service like Senders that basically white washes your email before delivering it to you.
The world’s most popular form of peer-to-peer messaging reached new heights in 2015, when users sent and received a collective 205 billion emails. Its growth isn’t slowing down anytime soon — analysts at the Radicati Group project that email users will exchange as many as 246 billion messages in 2019.