I linked emails to an Opportunity but no other user is able to see them.

In the Emails tab of the Opportunity window, first click the Refresh button to refresh your folder list.

Prophet CRM: Opportunity Manager - Public Folder Refresh View

Then, make sure that your Outlook folders are selected in the Emails tab and click Search. Prophet searches in all folders selected for the linked items.

Prophet CRM: Opportunity Manager - Public Folder Selection View

Once you set this for one Opportunity, you will not need to set this again for other Opportunities once you hit save and close.

Your email will now appear in the Emails tab. The folder it refers to is the folder in Outlook where the email resides. If you happen to move the email to another folder within Outlook, the folder name will be updated in Prophet automatically. If you permanently delete the email, it will no longer appear in Prophet.

Prophet CRM: Opportunity Manager - Sent Items View