Open Outlook
Go to File
Select Account Settings
Select Account Settings
Select your Exchange/Microsoft 365 account
Click Change
Select More Settings
Go to Advanced
Under Mailboxes, click Add
Type the shared mailbox name or email address
Click OK
Click OK again to close More Settings
Click Next/Apply, then click OK
Restart Outlook
If prompted, enter your credentials
In Outlook, expand your mailbox list
Confirm the shared mailbox appears under your account
If it does not appear, close Outlook and reopen, or wait for sync
To access the shared mailbox, drag it to Favorites or right-click it and select Add to Favorites (if available)