Outlook 2016 shared mailboxes not updating
However as explained in MS KB article KB2733062, this does not apply to shared mailboxes – which begin a full download on first use: For organisations who rely heavily on very large shared mailboxes, switching off caching of shared mailboxes would be a typical option for an on-premises Exchange installation; however latency over the Internet to Office 365 mean that although valid as a temporary workaround it is not a good solution.
Shared mailboxes aren't supported on mobile devices. A shared mailbox is a type of user mailbox that doesn’t have its own user name and password.
I’ve recently had a question from a colleague about solutions for using cached mode with very large (~10GB) shared mailboxes used by large numbers of users.
The problem the organisation is facing came to light after re-installing a number of machines as part of an upgrade to Outlook 2013, after a successful Exchange Online migration.
This first came to light when a new PC was provisioned for this employee and they logged into Outlook.
The inbox had literally thousands of emails in, all of which had been handled and cleared away previously.