Edit 6/15/2015:
We are starting to make this feature available again in Office 365. Note that the new shared mailbox Sent Items behavior is disabled by default. If you want to enable it for your us...
Updated Jul 01, 2019
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Hi Paul, thanks for sharing this in advance on the change going live. Are you able to give any indication of when we can expect to see this in Europe? We've always made people add Shared Mailboxes as 'Additional Account' rather than 'Additional Mailboxes'
in Outlook because of the extra features (signatures, Sent/Deleted Items etc) but have found this causes terrible problems with AutoDiscover when migrating to a hybrid Exchange Online setup. We might now ask all of our Outlook users (5k) to remove their additional
accounts and re-add their shared mailboxes using the additional mailbox method. Do you have any opinion on this? Are additional mailboxes in Outlook the long term solution that we should be trying to move to?