The client is Outlook 2010. It has almost a 12Gb mailbox. I want to run a series of archives to drastically reduce the size of the mailbox. Can I run the archives if Outlook is not in cached mode?
Outlook archiving moves the data to a separate file locally on your machine. Cached mode is a separate concept that refers to your machine having a local copy of data that is stored on your mail server for faster and offline access.
Please note that when you archive the data it will no longer exist on the server, so if you lose the archive file you will lose your archived data.