It´s interesting to see which OS or Email client your subscribers use. With this, you can follow and test your emails according to how software evolves.
All of this is also available inside of your Mailpro campaign statistics under contact details, where you can see what OS and software your contacts use to open their emails.
We insert invisible images in each newsletter in order to see when someone opens an email. This tells us which OS and email software is used. Apple devices download images by default, unlike Outlook. Therefore, Apple tends to have a higher rate.