The original email recipient/sender can create and link a task, event, workflow, or opportunity from an email. The icons below should display at the top of the email.
Other users that the emails are shared with will not see the options. Also, the user creating the activity must have their email visibility set to everyone in order for others to view the linked email.
After you have created the task, event, workflow, or opportunity, it will show that it is linked to that particular email:
