A colleague had a rule in Outlook so that; when they flagged a message for follow-up it was copied to a sub-folder (called Follow-up) and when they removed the flag, the item was removed from the follow-up folder, but still available in the inbox (or whatever folder it was moved to). This rule has disappeared in a move from Windows 7 to O365 (using desktop). I am unable to replicate the rule. Any ideas please?
I believe, you mean followup search folder that is available in To-Do Bar:
Right? If so, take a look at the following Microsoft Support article: https://support.office.com/en-us/article/Keep-upcoming-tasks-always-in-view-bcf25093-82f6-47f1-a7ec-cf9915186a99