Suppose you wanted to create an Outlook profile for a hidden mailbox and, for whatever reason, you do not want to unhide it from the Address Book just long enough to create it. All hope is not lost! ( Unless you are using Outlook 2016). You can do it using the LegacyExchangeDN.
1. Use adsiedit or your favorite LDP viewer/query tool and copy the LegacyExchangeDN of the hidden mailbox. ( I still prefer adfind to this day).
The LegacyExchangeDN value is a property of the user’s object in AD and will be in the form of: /o=Contoso/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=UserA
2. Create the Outlook profile. It will fail and you will be at the dialog box that shows server name and the users’ mailbox.
3. Remove the “=SMTP: User@contoso.com” value of the “Mailbox:” and paste the LegacyExchangeDN value you copied from Step1.
4. Hit Check Name and it should resolve and allow you to create the profile and access the mailbox.
This is with Exchange/Outlook 2013. This does not work with Outlook 2016 from what I have seen: