Cannot track emails in Dynamics CRM

I have enabled and configured embedded intelligence (Relationship assistant, Email engagement, Auto capture) following the steps mentioned here:

https://docs.microsoft.com/en-us/dynamics365/customer-engagement/sales-enterprise/configure-enable-embedded-intelligence#how-to-enable-embedded-intelligence

I have also enabled Email engagement. However, we haven't enabled OneDrive for Business since we do not need to follow attachments, just the emails (opened/clicked link). In Email Engagement section in Sales AI, we see the message

"Ready to use. No configuration required"

against Relationship assistant, Email engagement and Auto capture.

I understand Dynamics uses a hidden image to track if an email is opened and Images are not blocked in my email client.

Now I am not sure why the emails are not getting tracked. Can anyone share what could be the possible reasons?