In Outlook, take the following steps to access a shared mailbox:

• Go to File => click the big Account Settings button => Account Settings
• Double-click on your email address, then More Settings
• Go to the Advanced tab and press Add button
• Type in the name of the shared mailbox, for example sales
• Then exit out ( Ok => Next => Done => Close )

The shared mailbox will now show up in your list of folders on the left, usually down at the bottom of the list.