Make the root folder of the email that contains the folder to be shared visible to the user you want to share it with

This is undertaken in the email account that wants to share the folder

1. In Outlook, right click on the root name (this looks like the email address and is above the folders)

2. Choose Folder Permissions

3. Click Add

4. Search for the user you want to share a folder with  > Add  > OK

5. With the name highlighted  check the Folder Visible box under Other in the Permissions box, then OK