What are OST and PST?
Personal Storage Table (.pst) Files: These store your data right on your own machine, usually tied to POP3 email accounts or used when you want to archive stuff across different setups. You get to choose where they live, most often they land in C:\Users[Username]\Documents\Outlook Files. You’re free to move or copy them yourself whenever you like.
Offline Storage Table (.ost) Files: Built for IMAP, Exchange, or Microsoft 365 accounts, these hold a synced copy of whatever’s sitting on the server so you can keep using Outlook even offline. The system picks their location for you, typically C:\Users[Username]\AppData\Local\Microsoft\Outlook, and they’re tied to one specific profile, so you can’t go in and move them around yourself.
Both file types are really the backbone of Outlook, but neither is bulletproof, power outages, oversized files, or sync hiccups can all throw a wrench in things. Getting a handle on how they work is the key to keeping your data safe and to fixing problems quickly when they show up.
How Do Outlook Data Files Function?
At their core, Outlook data files exist to store and retrieve your information, and the way they do that depends on what each one is built for.
- Operation of .pst Files: These save your data locally without needing to check in with the server constantly, aside from maybe scheduled POP3 uploads. They run independently, syncing only when you tell them to or when you’ve set them up that way.
- Operation of .ost Files: These stay in constant contact with the email server, keeping everything lined up. The moment you write an email or set up a meeting, it lands in the .ost file and gets sent off to the server. If you’re offline, you can still browse what’s already there, and it’ll sync back up once you’re reconnected.
Significance of Outlook Data Files
Outlook data files play a pretty big role in how the app works, and they come with some genuine advantages.
- Offline Access: With .ost files, you can view or edit emails, calendars, and contacts even without an internet connection, and everything syncs up later. .pst files, since they’re local to begin with, just work offline naturally, no server required.
- Data Preservation: .pst files make backups easy; just copy them over to a USB drive or cloud storage, which comes in handy if your hardware ever fails. .ost files depend on the server, but you can still export them for an extra layer of safety.
- Performance Impact: Oversized files can drag Outlook’s performance down. Watching their size helps keep everything running smoothly and quickly.
- Troubleshooting Utility: If your PST file gets corrupted, you might start seeing errors, or you might find that your OST or PST file goes missing. Understanding how these files function makes it a lot easier to spot what’s wrong and fix it.
Management of Outlook Data Files
Here’s how you can handle the main tasks involved in keeping your .ost and .pst files under control.
Locating Data Files
.pst Files: In Outlook, go to File > Account Settings > Account Settings > Data Files. You’ll find the list along with the file paths, usually C:\Users[Username]\Documents\Outlook Files.
.ost Files: That same screen will show you where these are located too, often tucked away in C:\Users[Username]\AppData\Local\Microsoft\Outlook, though you won’t have much control over moving them.
Creating a New .pst File
Here’s how to set up a brand-new .pst file:
- In Outlook, click File > Open & Export > Open Outlook Data File.
- Pick an existing .pst or
create a new one by going to New Items > More Items > Outlook Data File.
- Give it a name, decide where it should be saved, and click OK to add it into Outlook.
Repairing Corrupted Files
Here’s how you can repair a corrupted Outlook file:
- Close Outlook completely.
- Find SCANPST.EXE in your installation folder (something like C:\Program Files\Microsoft Office\root\OfficeXX).
- Open it, select the corrupted .pst file or .ost file, and kick off the scan.
- If it turns up any issues, click “Repair” and let it run its course, then start Outlook back up.
OR
If you’re dealing with a severely corrupted OST or PST file that ScanPST couldn’t handle, go with a trustworthy third-party Outlook Repair Tool such as SFWare Outlook Repair Tool.
We’d suggest downloading and trying this tool with no hesitation, it works on a backup of your Outlook data file, so your original file stays untouched the whole time.
Download Now and try;
How do you fix Outlook data files using the SFWare PST Repair Tool?
Step 1: Download, install, and launch the SFWare PST Repair Tool.
Step 2: Choose a method for importing your PST file.
- Open Default PST file: Imports your default Outlook PST file.
- Select PST File Manually: Browse to and select a PST file by hand.
- Find all Your OPST Files: The software scans your whole drive and lists every Outlook data file it finds, so you can pick the one you need.
Step 3: Choose the scan, pick a destination folder for the repaired PST file, and click Repair.
Step 4: Check the results summary and save the file once you’re happy with it.
Also Read: How to Fix Corrupt OST File?
Reducing File Size
Here’s how to shrink your Outlook data file down through archiving:
- Go to File > Info > Tools for Accounts > Clean Up Old Items.
- Choose a folder (your Inbox, say), set a cutoff date for what counts as old, and pick a .pst file to move it into.
- Confirm the move, and your older data shifts over, taking some of the weight off.
- Keep up with habits like these, and your Outlook data files will stay steady and fast.
What is the difference between a PST file and an OST file?
A PST file is a standalone copy of your mailbox that lives only on your machine. An OST file is a cached copy of a mailbox that still lives on a server, usually Exchange, Microsoft 365, or an IMAP account. That is the whole distinction, really. Everything else follows from it.
Because a PST is independent, you can copy it, email it, move it to another computer, and open it in a fresh Outlook profile. Try that with an OST and Outlook will refuse it, or open it with nothing in it, because an OST is locked to the mailbox GUID of the profile that created it. Delete the account, and the OST becomes an orphaned file with no server to sync against.
Size matters here too. Outlook 2019 and Microsoft 365 both cap PST and OST files at 50 GB by default (ANSI-format .pst files from Outlook 2002 and earlier top out at 2 GB). Past that ceiling, Outlook starts throwing errors instead of saving new mail, which is usually the first sign a file needs attention.
Conclusion
Outlook data files sit at the heart of Microsoft Outlook, taking care of storing and retrieving your information no matter what kind of account you’re using. This piece has walked through what they are, how they work, why they matter, and how to manage them.
