When updating the authorized users list of a shared mailbox, it is important to note that only the owner of the mailbox may add/remove authorized users. Each shared mailbox can only have one owner.
Open Outlook.
In your Outlook toolbar, click on Find, then select Address Book.
In the Address Book pop-up window, choose Global Address List from the Address Book drop-down menu in the Address Book field (not Offline Global Address List).
Select the Advanced Find link.
In the Find dialog box, enter the mailbox name without @shu.edu in the Alias field. For example, to update the technology@shu.edu mailbox, enter “Technology” into the Alias field.
Click the OK button.
From the search results, double-click on the entry that displays as <mailbox>_ACL to view the list of individuals who currently have access.
Double click the "<mailbox>_ACL" entry to view the list of individuals who currently have access.
To add/remove authorized user(s) of the mailbox, select the Modify Members… button.
You can remove a user by selecting his/her name and choosing Remove.
You can add a user by choosing Add.... Then, use the search box to locate and select the name of the new user. Click OK to add your selection as a member of the mailbox.