Similar to Autocomplete settings, Outlook Categories are saved in a Stream_CategoryList_1_guid.dat file. The GUID is random, and looks something like this:
In order to restore Outlook Categories when creating a new profile, you can use the same approach required for restoring Autocomplete files. Basically, rename the old categories .dat file to match the DAT file associated with your new profile.
Here’s what my categories looked like before creating a new profile:
And here is the generic categories that Outlook comes with:
Not only am I missing my custom categories which prevents me from setting the categories I want on all my new emails, I’m also missing the categorization of my old emails – not an ideal scenario at all!
In this case, the category files might be the same size, so use your last modified date to give you an idea of which one you need to bring forward.
In order to import this Category list, make a copy of the one that you want to import, and then rename it to match the default one created by Outlook:
As you can see from the screenshot, I rename the default one to old, and then copy the name of the file to my clipboard. Rename your copy to match this (making sure that the file extension is still is .dat at the end), and voila!
Categories are back in place, and all is well with the world!
Update (July 2017): Going Deeper
After Kevin commented below on having multiple DAT files to try and sort through, I thought I’d take a look to see if there was a better way of figuring out which file holds your categories – trial and error is fine when there’s only a couple of files, but if you have a whole bunch, this gets annoying quickly. I had never tried opening these files in Notepad before, but essentially they’re just XML files, and so you can definitely open them up and find which files have your categories in them.
If I checked my current categories in Outlook, I can see I was actually missing these categories – I uninstalled and re-installed Office, and they ended up getting lost… perfect time to dig in and find my own fix!
So I opened both DAT files in Notepad ++ (if you don’t have it installed, you should – it’s amazing), and found my active file by finding the one that only had the MVP category:
I copy/pasted the lines that I wanted into my active DAT file – always make sure you keep the XML syntax intact – I noticed that my current category colour for MVP was “7”, or blue, which conflicted with my “Stratiform” category. I tried messing around a bit, changing the colour to orange, and replacing the orange line, but it wouldn’t stick when I saved the file:
So all I did from there was open the file back up again, undo my changes (love, love, love Notepad ++), and removed the orange line entirely, and added my MVP category back at the bottom, and all was well with the world again:
BOOM!
I’m sure smarter folks than I could tell me what specifically is happening in those XML files, and whether or not the order actually affects things – all I know is that my categories are back, and I’m in business again! 😀
Master & CmdR 
Great post! I am having an issue with a user where suddenly her categories are missing in Outlook 2016 (via Office 365) yet there are 21 Stream_CategoryList_1_xxxxxxxxxxxxxxxxxxxxxx.dat files. Any thoughts on how to recover her categories in Outlook? Thanks
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Hey Kevin,
wow… 21 is a lot! I’m guessing you’ve already tried using one from a date that you know had the correct categories? I decided to dig a little deeper into my own DAT files to see what I could find, and realized that I can open them in Notepad and read which file has the categories in it, which I’m willing to bet will help you find your missing categories as well! 😀
if you don’t have Notepad ++, I highly recommend grabbing it: https://notepad-plus-plus.org/. This tool is amazing for many reasons, but in this case, you can simply drag and drop all your DAT files into Notepad ++, and quickly scan your way across to find your missing categories. Also, if you edit one of your existing categories in Outlook and close it down, Notepad ++ will tell you which of your DAT files was just updated, and you can easily discover which of those 21 files is actually being used by Outlook. After that, simply replace the categories of the active file with the ones that were missing, and you should be golden!
In many ways, this might feel like a lot of work just to get someone’s categories back, but hey… we’re not superheroes for nothing!
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Thank you very much! That really helps. Do I rename the .dat file that is incorrect to .old and rename the one with the correct values to the same string name and restart Outlook? Or do I just edit the one in use and add the lines of code into it? Again, thank you very much. You are the superhero here, not me! This is awesome.
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Hey Kevin,
It doesn’t really matter, at the end of the day – the whole purpose around renaming .dat to .old is just to make sure you have your old copies to go back to if necessary (kind of a belt and suspenders kind of thing). Now that I see how the insides work, I’d probably just update the .dat file and save it – if it works, you’re done. If it doesn’t work that way, then fall back to the old way of renaming the file so that you have the right one being referenced by Outlook.
Glad this helped!
Jer
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Great post, but any idea if this can be made to work with AutoMapped Shared Mailboxes? the cat stream files obviously contains all mailbox cats, but a simple rename from old -> new filenames overwrite personal cats, doesn’t touch the cats associated to the shared mailbox.
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I just took a stab at finding the categories .dat file for an auto-mapped shared mailbox, and I was able to edit the file successfully in Notepad++. You should be able to identify the correct .date file and either edit it or overwrite it with your backed-up file.
If you’re having a hard time identifying which is the correct file to replace, go into your shared mailbox and change one of your categories, and exit Outlook. You can sort your .dat files by last modified, and you should be able to see which one needs to be updated or replaced. Take a stab at it and let me know how it goes!
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