This sounds ludicrous. 4 staff on a 20 user network are experiencing this problem. Not all emails in thier mailboxes are being displayed in Outlook. Also, Outlook says connected to exchange, but it says folder last updated "ages ago". Sometimes up to an hour prior to the current time.
If one removes cached exchnage mode and restarts, the other mails are then visible. The other mails are also visible via OWA. Its also not all mails after a specific time that are missing. Eg If there are 10 mails in the inbox today then 1,2,4,7,9 & 10 will display.