Consider the following scenario:
An Exchange ActiveSync (EAS) client is used to receive email items on a mobile device.
The EAS client tries to synchronize multiple folders at the same time, or a single folder when the device is being provisioned.
There are many new items available for one or more of the folders.
In this scenario, some email items are not available on the mobile device.
This issue occurs because the Exchange ActiveSync client did not receive the response from a sync request, and Exchange Server did not send the email items in the second request from the client.
To work around this issue, disable the synchronization of email items on the EAS client, and then re-enable email items for the client.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.