They are configured as Exchange accounts
Same answer would apply to an EX account - delete something from a device and it won't be seen in Outlook. Merely stating that it's a potential reason for Outlook not seeing a "few items".
For sake of clarity so as to not continue to go down a path that isn't applicable - are you saying that the user can see email items on a device which can't be seen in Outlook when looking at the <Inbox> of both devices (computer & whatever) at
the exact same time?
If yes, is there any pattern in terms of the "a few of them" between these 2 users as in "are the emails that go missing coming from the same place? Is there an Outlook A/V or Anti-Spam addin installed? May be an obvious question but has the
<Junk> folder been checked.
Karl Timmermans [Outlook MVP] "Outlook Contact Import/Export/Data Mgmt" http://www.contactgenie.com