Offload old messages to an Outlook PST/Data Folder

So many of us no longer have mailbox limits, thanks to Office 365 and cloud storage, but that doesn't mean that your mailbox can't be a bit overwhelming. Not only that, if your organization archives on a regular basis, you may have personal items being moved to those archives for all eternity! Why not create an Outlook Data File (also known as Personal Folders or PST files)? That way you can store your own stuff and keep it personal.