If you send a tracked email to a contact and you get a notification saying they read it, when should you call them?

Question: If you send a tracked email to a contact and you get a notification saying they read it, when should you call them?

• As soon as you see the first notification.
• After they respond to your email.
• After getting at least 10 notifications.
• After getting three or four notifications.

The right answer was: As soon as you see the first notification.