We have the same issue at work and the company deletes all 'old' emails periodically. With multi-year projects this is not helpful. I find outlooks archiver to be unreliable so I Create personal folders in outlook and file stuff there.
The newer versions of outlook/windows do seem odd and security block stuff you have already received or sent if you try and move or forward it. There will no doubt be a setting somewhere to mitigate this but since the company will have it locked down I haven't bothered to look. Hope you get a useful answer that I can attempt!