If you upgrade MobileX and use Office 365 and move from say
then you will need to uninstall the MobileX app on Outlook 365 and re-install.
Each client will also need to clear their caches depending on where they work.
With Outlook Web Access (OWA) on chrome they will have to clear their cache.
If using the Outlook clien users will have to clear their IE cache (as IE is what Outlook uses).