Outlook Activites not working in 'Background' process


I am having an issue with my unattended background bots.
I can make a simple background process, with only one activity - get outlook mail messages.
I leave it as simple as possible, using a blank account field, and “Inbox”. I test it in studio, and it works fine, the folders are all extracted. It works if I publish it and launch it from the orchestrator if I turn off the background process setting, so an unattended bot can run it find in normal mode.

However, turn background process back on, and Get mail activities continually returns this error when launched from orchestrator:

The specified folder does not exist

at UiPath.Mail.Activities.GetMailActivity.EndExecute(AsyncCodeActivityContext context, IAsyncResult result)
at System.Activities.AsyncCodeActivity.System.Activities.IAsyncCodeActivity.FinishExecution(AsyncCodeActivityContext context, IAsyncResult result)
at System.Activities.AsyncCodeActivity.CompleteAsyncCodeActivityData.CompleteAsyncCodeActivityWorkItem.Execute(ActivityExecutor executor, BookmarkManager bookmarkManager)

Nothing I seem to do fixes this, including opening and closing outlook beforem hand, with and without “open as administrator”. This is an issue, as this is part of a much larger Long-running orchestration process.

Thanks for any help!