The short answer: Before attempting any repairs, identify the account type. With IMAP, Exchange, and Microsoft 365, the primary copy of your email is stored on the server, while the local file is merely a cache—it can be discarded and downloaded again. With a POP account, the local copy is the only copy, so a corrupted file or failing disk can mean losing the entire mailbox. There is one more important point: most „missing" emails have not actually been deleted. They are hidden by a view, filter, the Focused and Other inbox tabs, a rule, or archiving. Before using any repair tools, make a separate copy of the data file while the email client is closed.
Missing email requires a completely different approach from missing photos. An email message can almost always exist in more than one place—and the order in which you check those places determines whether you make the job easier or overwrite the last remaining copy.
First: „missing" usually does not mean deleted
The most common causes have one thing in common: they do not move the messages at all—they merely stop displaying them.
| What the user sees | What actually happened | Where to check |
|---|---|---|
| Half the messages are missing from the Inbox | The Focused and Other inbox tabs are enabled | Switch to the Other tab; the feature can also be disabled |
| I can only see messages from the last few days | A filter is active, or messages are sorted by another column | Clear the filter and sort by received date |
| Messages disappear day by day | A rule is moving them to another folder | Review the rules and their destination folders |
| Older email disappeared all at once | Archiving or AutoArchive moved it | Check the Archive folder or the archive data file |
| An entire thread has disappeared | The conversation view is collapsed | Expand the conversation or disable the view |
| Search returns no results | It is searching only one folder | Expand the search to the entire mailbox |
| The mailbox is empty after reinstalling the system | The account was added again, but the old data file is not connected | Connect the original file instead of downloading everything again |
Archiving is particularly deceptive. Outlook offers it in two forms: the Archive button moves messages to the Archive folder, which is one of the standard folders for Microsoft 365, Outlook.com, and Exchange accounts. AutoArchive, however, moves older items to a separate data file that may not appear in the client at all. The user is convinced that the email has disappeared, while it is actually sitting in a file nobody thought to check.
The account type makes all the difference—and it is critical
This single distinction determines how serious the situation is.
IMAP, Exchange, and Microsoft 365. Messages live on the server, while the client keeps a local cache. In Outlook, this is an .ost file. It can be deleted, and Outlook will recreate it the next time it starts by downloading the content from the server. But there is another side to this: a cache is not a backup. When a message is deleted from the server, synchronization deletes it locally as well. The implications for businesses are explained in Microsoft 365 Does Not Back Up Your Emails.
POP. The client downloads email from the server and typically does not leave it there. All information is then stored in a single local .pst personal folders file. There is no second copy available for recovery—and this is precisely where „email recovery" becomes data recovery. If the file is stored on a disk that is beginning to fail, it may be the only existing copy of the company’s communications.
The difference between the two protocols is described directly in the documentation: POP3 and IMAP4 use two different strategies for where messages reside. With POP, they reside on the computer; with IMAP, on the server.
Where the email is physically stored
Outlook—the .pst file. According to Microsoft’s documentation, the default location is:
C:\Users\<username>\Documents\Outlook Files\The actual location may vary depending on the Outlook and Windows versions and on how the account or file was created. Instead of guessing the path, it is more reliable to ask Outlook itself: File → Account Settings → Account Settings → Data Files tab → Open File Location. This shows the exact path and how many data files are connected—and it often reveals an archive file that nobody knew existed.
There is another practical trap: Windows hides .pst and .ost extensions by default, and some folders along the path are system folders. Before searching manually, enable the display of hidden items and file extensions.
Thunderbird—the profile folder. Do not guess the path; Thunderbird can show it to you: Help → Troubleshooting Information → Profile Folder row → Open Folder. Inside, you will find subfolders for the individual accounts—email downloaded via POP and local folders in one branch, and the cache for IMAP accounts in another. Messages are stored in extensionless mbox files, where an entire folder is represented by a single file. Next to each one is a file with the .msf extension, which is only a search index. You can safely delete the index and Thunderbird will rebuild it; the mbox file is the one that matters.
One rule applies to both: never copy a data file or profile while the client is running. Close it, wait for the process to end, and only then make the copy.
Recovery within the client—the cheapest step and the only risk-free one
Outlook. Start with the Deleted Items folder. If the message is not there, check Recoverable Items: in the Deleted Items folder, select Recover items deleted from this folder, choose the messages, and confirm the recovery. This works with Microsoft 365, Exchange, and Outlook.com accounts because the server retains items for a certain period after they have been removed from the Deleted Items folder.
Thunderbird. A deleted message goes to the Trash—unless it was deleted while holding the Shift key. Something else is crucial, however: until the folders are compacted, deleted messages remain in the mbox file, merely marked as deleted, and are still physically present. Compaction is the moment when that space is actually reclaimed. Until you know that everything has been recovered, do not compact folders or empty the Trash.
A corrupted PST file: the scanpst tool
Outlook includes the Inbox Repair Tool, SCANPST.EXE, for corrupted data files. According to Microsoft’s documentation, Outlook 2016 and 2019 usually store it in:
C:\Program Files (x86)\Microsoft Office\root\Office16The tool checks the file and offers to repair it if errors are found. Before using it, however, take care of three things:
- Make your own separate copy of the
.pstfile. The tool creates a backup file during repairs, but relying on a single automatic backup when dealing with the only existing copy of your email is not sensible. - Scanpst repairs the structure; it does not recover content. It cannot restore a message that has been overwritten. It is intended for files that cannot be opened or open with errors.
- Never run it on a file stored on a failing disk. It writes to the file—and writing to faulty media is precisely what must be avoided during data recovery.
An .ost file is not repaired. With an Exchange account, you can simply delete it; Outlook will create a new one the next time it starts and download the content from the server. This is both faster and safer than attempting to repair a cache.
When the problem is no longer the email client, but the disk
You can recognize this by symptoms that affect the file as a whole rather than individual messages:
- Outlook freezes while opening the profile or reports that the file cannot be opened.
- Copying the
.pstfile or Thunderbird profile stops at a specific point and reports a read error. - The system reports cyclic redundancy check (CRC) errors, or the disk disconnects while in use.
- The file has an implausible size, or the entire profile directory has disappeared.
- The computer has slowed down, started clicking, or restarts while email is being accessed.
At this point, stop running scanpst and recovery software, and stop using the affected disk. Further attempts to read it can worsen the condition of the medium, while writing to it may destroy data that could still have been read. The procedure is the same as for any other deleted or lost files—the logic behind the first steps is explained in the article about deleted files in Windows. The correct next step is to make a sector-by-sector copy of the disk and work from that copy, rather than repairing the original.
Decision table
| Situation | Where another copy may still exist | First step | What not to do |
|---|---|---|---|
| Messages are missing from IMAP or Exchange | Server, Recoverable Items folder | Recover the items from the server | Delete the account from the client |
| POP account with an empty mailbox | Only in the local .pst file | Back up the file before doing anything else | Add the account again in a new profile |
| PST cannot be opened, but the disk is healthy | Original file | Make a separate copy, then run scanpst | Run scanpst on the only copy |
| PST is on a failing disk | Original file | Disconnect the disk and make a sector-by-sector copy | Run scanpst, CHKDSK, or recovery software |
| Deleted messages in Thunderbird | Trash and the mbox file before compaction | Search the Trash | Compact folders |
| Entire Thunderbird profile has disappeared | Disk or possibly a backup | Check the condition of the disk | Create a new profile on the same disk |
How to make this easier next time
- Know which type of account you have. With a POP account, the local file is the only copy and should be backed up just like accounting records.
- Back up the data file instead of merely exporting a few folders. In Outlook, back up the
.pstfile; in Thunderbird, back up the entire profile folder—with the client closed in both cases. - Do not assume that the provider backs up Microsoft 365 mailboxes for you. Retention policies and backups are two different things.
- Do not keep your archive in a single file on a single disk. Years of communication stored in one
.pstfile on one laptop is a classic scenario that brings people to us.
If it turns out that the problem lies beneath the email client—in the disk rather than the mailbox—leave the computer switched off and contact us or call 775 556 063. We perform diagnostics and recovery in our own laboratory in Brno. We have also explained separately when it makes sense to bring the storage medium in person; you can find approximate price ranges by fault type in our data recovery price list and an overview on the data recovery service page.
Frequently asked questions
Where can I find the PST file containing my Outlook email?
The default location is C:\Users\<username>\Documents\Outlook Files\, but it varies depending on the Outlook and Windows versions. Outlook itself provides the definitive answer: File → Account Settings → Data Files → Open File Location. Remember that Windows often hides .pst and .ost file extensions.
Can I delete the OST file if Outlook is behaving strangely?
Yes, for Exchange accounts. Outlook will create a new file the next time it starts and download the content from the server. This does not apply to email that is not stored on the server, such as messages in a POP account. In that case, no server copy exists.
What does scanpst do, and is it safe?
SCANPST.EXE is the built-in Inbox Repair Tool that checks and repairs the structure of Outlook data files. It writes to the file, so always make your own copy before running it. Never run it on a failing disk.
My older emails have disappeared, but I did not delete anything. Where are they?
They were most likely moved by archiving or AutoArchive to a separate data file, or a rule is moving them to another folder. Check the Archive folder, the list of connected data files, and your configured rules.
Why did my old email not download after reinstalling the system?
With IMAP and Exchange, it downloads from the server. With a POP account, nothing remains on the server, and the email stayed in the original .pst file on the old disk. You need to locate and connect that file—not configure the account again and hope for the best.
When does missing email require professional data recovery?
When the data file cannot be copied, the system reports read errors, the disk disconnects, or it makes unusual noises. Stop using the disk at that point—the recovery should be performed from a sector-by-sector copy, not from the original.
Sources
- Microsoft: Vyhledání a přenos datových souborů Outlooku z jednoho počítače do jiného
- Microsoft: Oprava datových souborů Outlooku (.pst a .ost)
- Microsoft: Obnovení odstraněných položek v Outlooku
- Microsoft: Prioritní doručená pošta v Outlooku
- Microsoft: Archivace v Outlooku pro Windows
- Microsoft: Automatická archivace starších položek
- Microsoft Learn: POP3 and IMAP4 in Exchange Server
Where to find us
ITHOPE is a company based in Brno, Czechia: we do data recovery from disks, RAID and NAS, PC and laptop service and IT for business, all in our own lab at Viniční 3587/216, 615 00 Brno.
Phone +420 775 556 063 (24/7 line). You can bring the device in person, or send it by courier (Zásilkovna, PPL).