Outlook Offline Address Book File Location
The Outlook Offline Address Book (OAB) files are stored in a hidden system folder on your Windows PC, typically under C:\Users\. The exact subfolder name is a long GUID (a unique identifier) that corresponds to your mailbox profile, and inside it you’ll find files like oab.xml and several .lzx data files.
Why Outlook Uses an Offline Address Book
When you use Microsoft Outlook with a Microsoft Exchange, Microsoft 365, or Outlook.com account, the Global Address List (GAL) is stored on the server. To let you browse names, email addresses, and distribution lists even when you’re disconnected (on a plane, in a hotel with bad Wi-Fi, or during a server outage), Outlook downloads a compressed copy of that directory to your local drive. This local copy is the Offline Address Book.
Outlook updates this cache on a schedule you control (default is every 24 hours) and uses it to resolve names when you compose messages, check free/busy info, or open the Address Book dialog. If the OAB fails to download or becomes corrupted, you’ll see errors like “The Offline Address List is not available” or names won’t resolve when you type them in the To field.
Where Exactly Are the OAB Files Stored?
For Outlook 2013, 2016, 2019, 2021, and Microsoft 365 (all running on Windows 10 or 11), the default location is:
C:\Users\\AppData\Local\Microsoft\Outlook\Offline Address Books\<GUID>\
Replace <username> with your Windows account name. The <GUID> is a long string of letters and numbers (e.g., 1a2b3c4d-5e6f-7890-abcd-ef1234567890) that Outlook generates per mail profile. Because the folder name varies, the easiest way to find it is to open File Explorer, paste the path up to Offline Address Books, and then open the only subfolder you see.
If you have multiple Outlook profiles (e.g., one for work and one for personal), each profile gets its own GUID folder. The folder is hidden by default because AppData is a hidden system folder. To see it, you must enable “Show hidden files and folders” in File Explorer’s View options, or simply type the full path into the address bar.
How to Find the OAB Folder in Your Own Outlook
If you don’t want to hunt through hidden folders, you can let Outlook tell you the exact path. Here’s how:
- Open Outlook and go to File > Account Settings > Account Settings again.
- Select the Offline Address Book tab at the top of the dialog box.
- You’ll see a list of OAB configurations. The Path column shows the full folder location for each profile.
This method works for Outlook 2013 through Microsoft 365. If the tab is empty, your account may not be configured to use an OAB (e.g., you’re using a POP3 or IMAP account without Exchange).
What Files Are Inside the OAB Folder?
Inside the GUID folder you’ll typically find these files:
- oab.xml – The manifest file that lists all the other data files and their version numbers.
- *.lzx files – Compressed data files that contain the actual address list entries (names, email addresses, phone numbers, etc.). Each file corresponds to a different part of the GAL (e.g., one for user objects, one for distribution lists, one for rooms).
- *.bin files – In some Outlook versions, these are the uncompressed or partially processed data files.
The files are not human-readable. They are in a compressed binary format that only Outlook can interpret. You should never manually edit or delete them while Outlook is running, as this will corrupt the cache and force a full re-download.
How to Fix a Corrupted or Missing OAB
If you see errors about the offline address book, or if names don’t resolve when you’re offline, the most common fix is to force Outlook to rebuild the OAB from scratch. Here’s the standard procedure:
- Close Outlook completely.
- Open the OAB folder using the path from the Account Settings dialog (or the manual path above).
- Delete the contents of the GUID folder. Don’t delete the GUID folder itself, just the files inside.
- Restart Outlook. It will detect the missing files and download a fresh copy from the server.
If that doesn’t work, you can also trigger a manual download: In Outlook, go to Send/Receive > Send/Receive Groups > Download Offline Address Book. Check the box for “Download changes since last Send/Receive” (or leave it unchecked for a full download) and click OK.
Another common issue is that the OAB folder path contains a very long GUID, and if your Windows username has spaces or special characters, some third-party backup tools fail to include it. This isn’t an Outlook bug, but it explains why your OAB might be missing after a system restore.
How to Move the OAB Folder to Another Drive
Some users want to move the OAB folder to a different drive to save space on the C: drive (especially on small SSDs). Outlook doesn’t provide a simple GUI option, but you can change the location via the Windows Registry. Here’s the general method:
- Close Outlook.
- Press Win+R, type
regedit, and press Enter. - Navigate to
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Offline Address Book(for Outlook 2016/2019/2021/365; the version number may be 15.0 for Outlook 2013). - Look for a string value named
Path. If it doesn’t exist, create a new String Value and name itPath. - Set the value to your desired folder, e.g.,
D:\OutlookOAB. - Close the Registry Editor and restart Outlook.
Outlook will create the folder if it doesn’t exist and download the OAB there. Note that editing the registry incorrectly can cause problems, so back up the registry first. Also, this method works for the classic desktop version of Outlook, not the new Outlook for Windows (which uses a different sync model).
Frequently Asked Questions
Why can’t I see the AppData folder?
AppData is hidden by default in Windows. To view it, open File Explorer, click the View tab, and check the box for Hidden items. Alternatively, type the full path into the address bar and press Enter — Windows will take you there even if it’s hidden.
What is the difference between the Offline Address Book and the Outlook data file (.pst/.ost)?
The OAB stores only address list information (names, email addresses, distribution groups) for offline lookup. The .ost file stores your mailbox content (emails, calendar items, contacts you own). They are separate. The OAB is a read-only cache; the .ost is your working copy of the mailbox.
Can I delete the Offline Address Book folder to free up space?
Yes, but Outlook will simply re-download it the next time it connects to the server. If you are permanently offline and never use the GAL, you can disable the OAB in Account Settings > Offline Address Book, but you’ll lose the ability to look up names when disconnected.
Why does the OAB folder have a weird name with numbers and dashes?
That’s a GUID (Globally Unique Identifier) that Outlook assigns to each mail profile. It ensures that multiple profiles on the same machine don’t overwrite each other’s OAB data. It’s normal and you should not rename it.
Does the new Outlook for Windows use the same folder?
No. The new Outlook for Windows (and Outlook on the web) uses a different sync engine and stores address book data in the cloud cache, not in the classic Offline Address Book folder. The classic desktop Outlook (Outlook 2013–2021, Microsoft 365) is the one that uses the OAB folder described here.
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