Been evaluating grommunio for about 6 months now. Suddenly today, all my messages were gone in outlook in TWO of my grommunio mailboxes. One mailbox had some recent items in inbox from today but that's all. I switched folder some times and restarted outlook, and then suddenly only 1 last item was available. Outlook connection status showed everything as online, so there must be some kind of desync. I waited a couple hours to see if it would fix itself. I got some new emails, but anything older than today never came back. Ended up renaming the .ost files (it was only 16MB so all emails were clearly gone) and everything synced fine again.
I had cache setting set to "all" on one account and "1 year" on the other. I had 2 more accounts in outlook (office 365, 1 year cache) they were not affected.
Never had this happen in 5 years with regular microsoft exchange server, so the cause is likely grommunio related.
I can supply the corrupt .ost file privately on request if required.
Thanks,
Michael