When archiving in Outlook, it is often useful to archive by the date of receipt for items. It is not a widely known fact that Outlook archives email messages by the last modified date. This is generally not an issue, unless you were performing some inbox cleaning out and moved an item from 2012 to another folder. At that point, the last modified date becomes the date of when you moved the email. So when you attempt to archive your mailbox, this item does not get archived.
The following KB article explains how you can change this default behaviour in Outlook – http://support.microsoft.com/kb/2553550
According to the KB article, by default, Microsoft Outlook 2010 and Microsoft Outlook 2013 archive different items based on the item type, as follows:
- Email message: The received date or the last modified date and time, whichever is later.
- Calendar item: The last modified date and time or the actual date that an appointment, event, or meeting is scheduled for, whichever is later.
- Task: The completion date or the last modified date and time, whichever is later. Tasks that are not marked as completed are not archived. Tasks that are assigned to other users are archived only if the status is completed.
- Note: The last modified date and time.
Journal entry: The date when the journal entry is created or the last modified date and time, whichever is later.
- Contact: Not archived.
To change this behaviour, you can create or modify the following registry setting.
Outlook 2010 – HKCU\Software\Microsoft\Office\14.0\Outlook\Preferences
Outlook 2013 – HKCU\Software\Microsoft\Office\15.0\Outlook\Preferences
Edit or Create a new DWORD value, ArchiveIgnoreLastModifiedTime, with a value of 1
IMPORTANT: You must restart Outlook after this change has been made.