in Opinion

You might be aware that using File > Open > Other User to open a shared mailbox will only show you the mailbox’s Inbox folder.

Here’s how to have full access using an Exchange Online connection (it works with IMAP/POP/SMTP if you have those enabled as well, but most will prefer Exchange):

  1. Go to Preferences > Accounts
  2. Add a new account
  3. Enter you shared mailbox full email
  4. Manually choose Office565 as the email provider
  5. You will now be presented with the Office365 login popup. Under the password field choose Use another account
  6. Enter you own username (Office 365 email) and then your password.
  7. And that’s it! You should have your Shared Mailbox fully available