Microsoft Outlook Archiving Quirks
While Outlook should work as explained above, you might have noticed a few oddities in the way that your emails are archived, such as Outlook not archiving them unless the date of a message is set in the future.
This probably won’t affect you in most cases, but if the email in question has been sent, received or modified on a system with an incorrect date setup in the operating system, then when the message arrives on your computer there is a chance that it will not be included in the archive program. If this is the case then you will need to be wary of bulk deleting of messages that you expect to have been automatically archived.
Unfortunately there is no way around this particular Outlook quirk. The Sent date is applied by the sending computer or mail server, and the Received date from the header that is created when the email is routed to your computer. The Last Modified date, meanwhile, is set when you perform an action on the message such as moving it to a new folder.
If any of these dates are out of sync on the host machine, then this will prevent the item from being archived, as AutoArchive only works on messages with dates set in the past, and the tool checks all three of the date types listed above.
There isn't really an awful lot you can do about this problem, other than reporting it to the administrator of the email server concerned and hoping that that they are able to resolve it.