If you’ve ever used Outlook’s archiving feature, you may have noticed that a lot of emails that should have been archived are left behind. For example, you tell it to archive anything older than Dec 31, 2014, yet emails older than that still remain in the original folder.
The reason for this is that Outlook’s default behavior is to archive based on the “Last Modified” date, which means that if you made any sort of modification to the email after the specified archive date then email won’t be archived. What’s a modification? It could be something as simple adding or removing a flag. Supposedly some anti-virus apps also cause this date to change.
I think everyone’s intuitive understanding of the way archiving should work, is that the mail is archived depending on when you got/sent it, no matter what you did with it afterward. Luckily, you can tell Outlook to use this more intuitive method by adding a simple entry to your registry.
The registry setting is called ArchiveIgnoreLastModifiedTime, and it’s registry location depends on the version of Outlook you’re using.
For Outlook 2007, please follow Knowledge Base article 2500686. Make sure you have at least SP3 installed.
For Outlook 2010 or 2013, please follow Knowledge Base article 2553550.