When you connect an email account, it is marked as private by default, meaning that the person who connected the email is the only one who can view the emails in the unmatched folder. Email privacy settings are in place for cases of personal or work emails that wish to keep the contents of their inbox private. Private emails display a privacy notice in the subject field.
To stop the privacy notice and allow all Users to view these emails, the creator of the email account must visit the privacy settings and turn off their email privacy.
Users can also request access to private emails. To do this, the User must hover over the email in question and press 'Request Access'.
The request will be sent to the owner of the email account via email with a notification to change their privacy settings.
Here is a Knowledge Base article explaining how to change your email privacy settings.