*Rule in/out the workstation itself = Recreate the users Outlook profile within another user profile on the same and/or a different workstation to see if it's reproducible. * Rule in/out the mailbox = If the user is has access to a shared mailbox, make changes to that, and see if those are married up to Office365. If, like me, you hate the in-built mail app, try Thunderbird instead.

Check and see if the issue is reproducible. * Rule in/out Outlook/Office = Configure the users mailbox using the in-built Mail app in Windows 10. * Rule in/out server-side issues = Have the user makes some changes on their phone and see if those are married up to their Office365 mailbox. Thanks in a new one on me, but the old support rule of divide and conquer should serve here as well as it usually does.

The only issue appears to be changes they make aren't showing in Office 365. I've tried checking whether cached version is used (it is not), recreating the profile, whether Outlook is updating (account is selected in Send/Receive Group) and the end user can send/receive email fine, there is no delay there.

I've been searching for some time on a possible solution to this but can only find reference to 'local client not updating from cloud', which doesn't help as this is 'cloud not updating from local client'. An admin assistance also has access to their mailbox (not cached) and they also do not see any changes. If they check on their phone, the inbox looks different and any change that was made is not shown. The changes they make are generally filing email away to sub folders or deleting them. They are accessing a local Outlook 365 client and any changes they make on their client are not being sync'd back up to Office 365. I have a client who is having issues with Office 365.

Office 365 outlook 2016 sync issues