When tracking the behaviour of an email message, a tracking pixel or beacon is typically employed. The pixel or beacon activates when the email is opened, acquiring data on the email recipient (such as their IP address).

1. Email Tracker Chrome Extension | OpenedOrNot by 500apps
A tracking pixel or beacon is frequently used to monitor the activities of an email message. When
an email is opened, a pixel or beacon is activated, and information about the email receiver (such
as their IP address) is retrieved. Email tracking can be used to determine whether an email was
opened, how long it was seen for, and where it was viewed.