If you want to share an email folder from your Exchange mailbox, there are a couple of steps for doing so. The folder you intend to share, and the folders leading to that location, must have their permissions modified.
As an example, User "NY Test User" needs access to TJ Williams' "365 Defender Alert" email folder:
Top of information store: must have "folder visible" for target user (you can set this as "Default", I don't recommend it.)
Inbox: must have "folder visible" for target user. Same configuration must be set for any other folders in the folder chain, before you get to the folder you intend to share.
Folder you intend to share: set necessary permissions. Editor should be fine. Set "Delete Items" as "own". This way user can delete their own items, not yours.
Using Outlook on the Web as an example.
- Right-Click on "Folders"
- Select "Add Shared Folder or Mailbox"
- Type in the name of the user who shared the folder with you
After some time has passed you should see the shared folders. You may, at first, only see the username of the person who shared the folder: