Outlook 2016 Cached Mode connection to Exchange Online no new mail


We have started to migrate our users from on-prem to Office365. The migration provides the end user with a new machine (Windows 10 Anniversay) and Office2016 deployed via SCCM using click to run package. During the initial cache backfill users are not receiving new email, instead they are having to manually request a Send / Receive folder update to receive email on the Exchange server. They are more aware of this problem because the Outlook client on IOS is receiving the new email in a timely fashion.


If the initial syn period is dropped to a few days then the new email appears in the Inbox as expected (even though folders are still backfilling into the cache). Once the cache is completely backfilled Outlook also returns to the expected behaviour. Mailboxes are in the order of several GB and backfill is set to 12 months


Has anyone else experienced this issue? It feels like either the new mail notification is not being received by Outlook to check Exchange Online, the new email is being received but not presented in the client, or some form of throttling is occuring either server side or client side. We have a case open with Microsoft Premier but looking for community experience.



3 Replies

Outlook 2013 and newer have the "fast access" feature that should ensure new messages are displayed and calendar is updated, you can read more about it here:


And here are even some more details along with the differnt GPO settings allowing you to properly prepare for such scenarios:

@Vasil Michev thanks for the response and links, I would have a closer look at our GPO and the client behaviour. As you say based on "fast access" the expected behaviour should not be what we are observing. Will update with more info after testing



best response confirmed by Jeff Medford (Community Manager)
@Vasil Michev I have now been able to reproduce the issue on a technical laptop. It looks like Outlook is behaving as designed but for the benefit of others here are my observations. Starting Outlook for the first time means a 12 month synchronisation of emails to cache mode by default. The first folder to sync is calendar then Inbox. I used Outlook online on the same machine as the candidate mailbox whilst the cache was backfilling sent a new message. The message appeared in Outlook online but not in Outlook. However, Outlook was still synchronising the Inbox, the users in question tend to be stackers rather than filers so whilst the mailboxes are not huge they have most of their items residing in the Inbox. Whilst backfilling the Inbox new emails are not displayed. Once the Inbox is synchronised then new email is displayed automatically at the top of the Inbox, any further emails are also now displayed in the Inbox (focus of backfill has moved on to other folders) Observing the behaviour makes sense as to what is going on, the issue is exacerbated because the branch office doesn't have the best of internet links. Our mitigation is to only sync three days worth of email on the first synchronisation, this ensures basic functionality can be confirmed with the user and we can hand back the machine. Our advice is then to leave the machine in the office overnight and we change the synchronisation period to 12 months. Thanks for your help and pointers Paul