When Outlook is running in cached mode and the users is connected to different shared mailboxes or public folders, Outlook may cache also the content from the other mailboxes in local OST-file. This can be result in a very very huge OST-file. SSD can run out of disk space or Outlook will be much slower than without caching the external mailboxes
If you want to create an Outlook-Profile which points to a Mailbox which is actually hidden in the adressbook you wil get an error from Windows/Outlook.
Unchek the hidden-option from Exchange-Mailbox-Properties for a moment.
Please note: Sometimes the adressbook generation only runs every 24 hours or something else
After creating a Outlook-Profile for the mailbox you can hide the Mailbox in Exchange again. It will also work afterwards
Instead of the Mailadress or UPN (UserPrincipalName) you can use the legacyExchangeDN which Outlook will accept to create a Profile from a hidden mailbox.
You can find the legacyExchangeDN in the ActiveDirectory-Object from the hidden mailboxuser. Please enable the advanced features view, open the user properties, change to Attribute Editor –> copy the principalname from legacyExchangeDN to the clipboard and paste it into the user-field in the profile-creation-wizard from Outlook/Windows. You will see, the wizard will accept the user although the mailbox is hidden from adress list.
After finishing the wizard you can open Outlook with the hidden mailbox-user. Thats all!