I have replicated this problem across Outlook 2003, 2007 and 2010.
When manually archiving a mailbox by date, it doesnt reliably move all the emails in subfolders to the archive as expected.
I have done a bit of reading and everyone points to the modified date as the date it archives by and *not* the received date. But that only explains *some* of the emails not moving. There is a larger majority that dont get archived that I am yet to find an explanation for.
E.G. a subfolder in the inbox has emails with received dates rangeing from 2011 to 2009.
I archived from Jan 1 2011 and none of the emails got moved.
The modified date for a lot of the emails match the received date and there is a small quantity where the modified date is new than the received date.
However none of the emails were archived.
What am I missing?