Of course there have been many articles written about robocalls and how they are becoming a pain. These primarily are from marketers wanting to sell you something. Well, here is an article about a somewhat similar situation of what marketers are up to in emails: embedding trackers in their email so they'll know when you open one from them.
Here's how it might work: say I've ordered wine from a winery in the past, and they send me an email with a pricing incentive to order more wine. I open the email and read their offer. Suddenly my phone rings. I answer and I hear a nice voice saying, "This is the ABC Winery, and how do you like our new pricing offer?" What? How did they know I just opened their email? By an email tracker. The article explains more about how this works.
Now, so far I've not been bothered by an email tracker -- and you probably haven't been either -- but this is just something for all of us to be aware of. I use Gmail, and perhaps Google is doing some screening of emails to prevent trackers. Maybe/maybe not.