Your aim is ultimately to archive your mail store to cloud. What if you could archive your email directly out to the cloud in real-time through an archiving tool. Not a file based cloud storage like dropbox but a mail cloud like GMail. Outlook Mac Archive Tool! supports that feature, called Cloud Archive.
The advantage of archiving to a folder in a GMail account is your mail is always accessible through a web interface, searchable and safely backed up in free storage. You could use multiple Gmail accounts if you have excessively large mail stores (e.g. one for each year of mail).
The tool also supports the more common archiving operation of automatically moving your mail (over a certain age) from your online working email account down on to 'On My Computer' preserving your folder structure. It's your choice then if you want to archive it to a Mail Cloud automatically or a File Cloud by pointing it to your file folder: /Documents/Microsoft User Data/Office 2011 Identities