To send an email with tracking in Polymail, simply click the blue lightning bolt ⚡️ icon while composing your message.
This enables tracking, so you'll get notified the first time your email is opened.
You can also opt to receive notifications every time the email is opened. All opens will be visible in your Activity Feed and by hovering over the lightning bolt icon next to the message.
After your email is read, the lightning bolt icon will turn blue to let you know.