Just moved a client into Exchange Online. One of the reasons they wanted this solution was because they have a large Contacts List that needs to be shared. To accommodate this need, we created a shared mailbox and uploaded all the contacts there.
At the client side, we add the shared mailbox to the list of additional mailboxes opened during startup, and we're now able to access those contacts without a problem. BUT we can't seem to get that shared Contacts list to show up when we're trying to send a message. We can open a new message, click To, and all that shows up are the Offline Global Address Book, the users' own Contacts Lists, etc. We can't seem to get the shared list to show up.