Windows 10 | Outlook

These steps assume the following:

You are a Microsoft Exchange user on Office 365
A shared mailbox has been created in the Microsoft Exchange/Office 365 system and you have been granted rights to access the resource.
The shared mailbox has not been migrated to Office 365

Open Outlook
Navigate to File > Account Settings > Account Settings...
Select New
In the "E-mail Address" field, enter the email address of the shared mailbox you want to add, then select Continue
Select Advanced Options
Select Let me set up my account manually, then select Connect
Select Exchange
If prompted to sign-in, select More choices, then Use a different account
Enter your Andrews email address and password; not the email address of the shared account.
Select OK
Select Next when asked to configure Offline Settings, then select Done
Select Close and restart Outlook.
When Outlook prompts for login, remember to always authenticate shared mailboxes with your Andrews email address and password.