This is how to show a shared mailbox (e.g. office@company.com) in Outlook. Requirement: access to the mailbox has been set up.
Outlook (classic)
The mailbox usually appears automatically in the folder list, at the latest 60 minutes after access is granted and Outlook is restarted. If not:
Open File › Account Settings › Account Settings ….
Select your own account and click Change ….
Open More Settings › Advanced tab.
Click Add …, enter the mailbox address and confirm with OK.
Finish with Apply › OK › Next › Finish and restart Outlook.
New Outlook and Outlook on the web
In the folder list, right-click Folders or your own account name.
Choose Add shared folder or mailbox.
Enter the mailbox address and click Add.
Outlook for Mac
In the menu bar, open Outlook › Settings › Accounts.
Select your own account and open Delegation and Sharing.
Choose Shared With Me and click + at the bottom.
Enter the mailbox address and click Add.
Outlook app (iPhone and Android)
Open the Outlook app (App Store, Google Play) and tap your profile picture in the top left.
Tap the icon for adding an account (envelope with plus).
Choose Add Shared Mailbox, enter the address and confirm.
Note: If classic Outlook gets slow with shared mailboxes, see “Switch to online mode – Outlook (classic)”.