I asked this question on Microsoft Community and had no useful answers. I am hoping you lovely people can help.

tl/dr: how do you force Outlook client to upload contents of .ost when already-running sync process appears stalled?

As a company we have migrated to O365 last year. Most users have had a smooth transition.

One of our users has just had a PC refresh so the contents of their local .pst on the old PC needed to be moved to the new PC. We copied the contents of their local .pst archive into the 'Archive' folder within their account as we have done for numerous other users. On the old PC where this copy took place all the contents appear to have copied across successfully from the .pst to the account folder (.ost). However, on the new PC that this user is signed in to, the Outlook desktop client does not show the contents of most of the transferred folders and sub-folders. All of the folder/sub-folder names are visible in the second PC and a very few sub-folders have contents.

On the old PC the status message at the bottom of the Outlook client says "This folder has not yet been updated" and "Connected to Microsoft Exchange". On the new PC the status message is "This folder is up to date" and "Connected to Microsoft Exchange". Both Outlook desktop instances are running in Cached Exchange mode. This user is a very busy manager who was unable to stop moving emails into the 'Archive' folder and immediately started to do so as soon as the new instance of Outlook was running on the new PC, so there was never an opportunity to simply copy the .pst to the new PC from the old one (which would have been my preferred solution). This means that at all costs I must preserve the state of both machines.

To clarify the time line:

On old PC:

  1. The user stopped moving dealt-with emails to the .pst archive and then copied the contents of the .pst archive to 'Archive' folder in account using Outlook's 'copy' dialogue.
  2. This copy process took a solid half-hour and presented a separate progress bar for each sub-folder (The .pst was 11.5GB).
  3. On completion of the copy process the user continued work by moving dealt-with emails to the 'Archive' folder in account.
  4. The status message presented "updating " with foldername changing every few seconds, for several hours.
  5. The PC was left on, with Outlook running, overnight with the status message still changing.
  6. The user starts using the new PC during 4.
  7. The following morning the status message on the old PC Outlook shows as "This folder has not yet been updated" when clicking on any of the folders or sub-folders in the account's 'Archive' folder.

On new PC:

  1. User continues work and keeps moving dealt-with emails to 'Archive' folder structure that has shown up in Outlook client, as soon as it was available.
  2. The following morning they notice that the 'Archive' folder has limited contents even though each folder and sub-folder shows "This folder is up to date".

On both PCs the Outlook client is manually forced to 'Update Folder' from the Send/Receive tab, even running this command on each individual sub-folder in the 'Archive'. On the old PC the status message remains as "this folder has not yet been updated" and on the new PC the status message is "This folder is up to date"

In each instance of manually updating a sub-folder on both PCs (obviously, the old one first), no changes in content are observed on the new PC.

The office has a synchronous 100Mb fiber link to the outside world so the data transfer is not being throttled.

New profiles are not an option.

Further to this, (and proving it is the syncing-up-to-the-cloud that is the issue) opening the account in outlook.com and using Outlook on the web, the contents of the 'Archive' folder show exactly the same as on the new PC. The sub-folder structure is in place and a few emails in some of the sub-folders, but the majority is missing. I cannot risk running a re-profile on the old PC as that would simply drag down the contents as the cloud sees them, already proven to be missing data. Re-profiling on the new PC would be irrelevant. What I want to know precisely, is how to force Outlook to upload the contents of the .ost on the old PC into the cloud. It seems that any of the commands available on the 'Send/Receive' tab do not achieve this.

One suggestion was to change the setting on the old PC Outlook from 'Cached Exchange mode' to un-ticked, therefore using 'Online' mode. From my reading of how this mode works suggests it will force the Outlook client to look only at what is on the server, losing the un-synchronised data currently in the .ost file.

  • If you are Exchange/IMAP account, the messages should be synced from old client to server and then synced from server to new client. This will take a lot of time, any mistake will make this process broken. To check whicn period which stage has a problem, please log in to your web mail and see if the messages have synced to the server completely.
    – Aidan
    Nov 12, 2019 at 7:56

1 Answer 1


Answering my own question after much further research.

The short answer is that the sync process was not in fact stalled. It is just plain slow; slow like a laid back slug on valium.

An 11.5 GB .ost file took nearly 6 days to complete, but is now showing a status message in Outlook as 'All folders are up to date'. Clicking on individual sub-folders show 'This folder is up to date' Comparing the folder contents across the old PC, office.com and the new PC show all now have the same content.

Microsoft have severely throttled the upload of content to the cloud as a policy, which only 365 domain super-admins can over-ride by manually uploading a data-file and associating it with an account. Thankfully, in my organisation we have such a super-admin and all future .pst uploads over 4GB will go through him (much to his chagrin).

Unfortunately, unbeknown to me, our European Managing Director decided to move his .pst archive contents to his account. That .pst is over 50GB so I am anticipating a couple of weeks for it to synchronise. Sadly, he used the 'move' command rather than the 'copy' command so the archive contents are effectively unavailable until complete.

Advice to all if attempting this - use 'copy' not 'move'

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