These days, Outlook Categories are saved within the PST data file. If you move the PST to a new computer, the categories will move too. Exchange Server saves categories with each user mailbox and they show up automatically when you login (even with Outlook Web Access).
Backup and Restore
Even so, there’s occasions when it’s good to export your category settings and import them in another version of Outlook. You might be moving to a new PST file to fix errors in the old PST (still necessary sometimes) or share your categories with someone else.
Alas, there’s no import/export category option for Categories but you can fake it. In short, make an Outlook item (most easily an Outlook Note) and set on that item all the Categories you want to export. Then save a copy of that item to Explorer (drag and drop to make a .msg file). Take that .msg file and import it into another copy of Outlook (this time, drag and drop into Outlook).
Finally, go to the top of your mailbox in the folder list (above and left of Inbox), right-click and choose Properties. Click on ‘Upgrade to Color Categories ….’
Upgrade to Color Categories
The ‘Upgrade to Color Categories’ option sounds like a one-off thing for conversion from the old Categories to the new color-tagged ones. But it’s actually more useful than that.
Upgrade to Color Categories will rebuild the Master Category list be scanning the existing Outlook items and putting any categories into the master list.
There’s also a command line option /remigratecategories to do this
Unfortunately, this can take some time to do as Outlook scans all items in the mail store. There’s no way to limit the category scan to a smaller group of items.
Frankly, it’s sometimes faster just to re-type the categories into the Master Category list, especially if you only have a few categories to move across.
If you’re serious about Outlook Categories, you might like to try Category Manager an add-in for Outlook 2013, 2010, 2007, 2003, 2002/XP and 2000.