I have an exchange online (plan 1) account and I have outlook 2016 desktop. I connected my outlook 2016 to the exchange online account and I set 'use cached exchange mode to download email to an outlook data file' to 'all'. Outlook is not syncing all messages, lots are missing. For instance, I have emails in a sub folder of my inbox from july/2020. In outlook, the folder is there but no messages in that folder. If I do 'send/receive all folders' or 'update folder', is always shows 'all folders are up to date', but this is not correct.
I have deleted the outlook account, then re-added it, no help.
I have done a compact on the data file, no help.
How do I get outlook to sync all emails?