Emails missing from Outlook or a PST? Check these causes before you assume they are lost

When old emails, a folder or an attachment disappear from Outlook, the mail is usually still there. Outlook may have downloaded only the last year, a view may be hiding it, an archive policy may have moved it, or search may not be looking in the file that holds it. Real loss, from deletion or file damage, is the least common cause, and it is worth ruling out the others first, because some fixes for damage (repairing a PST) can make things worse.

The checks below go from most to least likely. Each one says what you would see, how to confirm it and what to do. Menu names are for classic Outlook for Windows (Microsoft 365, 2021, 2019, 2016) unless marked new Outlook, the newer app that replaced Mail and Calendar.

First: is it your mailbox or a PST file?

Two different things can be “missing”:

• Mail in your mailbox (Microsoft 365, Exchange, Outlook.com, Gmail through IMAP). The original copy lives on the server; Outlook shows a local copy.
• Mail in a PST file (an Outlook Data File you opened, imported or created by archiving). The PST is the only copy, unless you kept others.

The first group of causes below applies mainly to mailboxes; the rest apply to both.

1. Outlook has not downloaded older mail

What you see: folders seem to stop a few months or a year back, and item counts are lower than expected.

In classic Outlook with an Exchange or Microsoft 365 account, Cached Exchange Mode keeps only part of the mailbox in the local file. Microsoft’s article on only a subset of items being synchronized explains that by default Outlook keeps 1, 3 or 12 months depending on disk size: 1 month on disks of 32 GB or less, 3 months up to 64 GB and 12 months above that. The older mail is still on the server, and the bottom of the folder shows:

There are more items in this folder on the server. Click here to view more on Microsoft Exchange

To confirm and fix: File › Account Settings › Account Settings, double-click the Exchange account, and move the Mail to keep offline slider (called Download email for the past in later versions) to the period you want, or to All. Outlook asks to restart and then downloads the rest. The setting does not limit calendar, contacts or tasks, and Microsoft 365 group folders sync at most one year whatever you choose.

New Outlook has no Cached Exchange Mode. Its offline copy is set in Settings › General › Offline › Days of email to save, with 7, 30, 90 or 180 days and 30 as the default, according to Microsoft’s working offline article. Online, everything still shows; offline, only that window does.

2. A view is hiding it

What you see: a folder shows fewer messages than its count, or the mail you expect is not in the list.

• Focused Inbox. Mail Outlook judges less important goes to the Other tab. It is easy to miss after a new install.
• Conversations. With View › Show as Conversations on, replies are folded under one line, and conversations can include messages from other folders.
• A filter on the view. View › View Settings › Filter can hide items by date, sender or read status. View › Reset View returns the folder to the default.
• The IMAP view after an import. If you exported mail from an IMAP account to a PST and imported it elsewhere, the folders can look empty. Microsoft’s article on mail not showing after importing a PST says: “The email messages aren’t lost, but they are hidden from view.” Select View › Change View › IMAP Messages.

3. AutoArchive moved it to archive.pst

What you see: old mail is gone from the Inbox and Sent Items in a profile that has been in use for years.

AutoArchive is a classic Outlook feature that moves items past a certain age into a separate PST. Microsoft’s AutoArchive settings article gives the default location as C:\Users\YourUserName\Documents\Outlook Files\archive.pst and the default ages as six months for the Inbox, Drafts and Calendar, two months for Sent Items and Deleted Items and three months for the Outbox.

To confirm: look for Archives in the folder list. If it is not there, find archive.pst and open it with File › Open & Export › Open Outlook Data File. A folder’s Properties › AutoArchive tab shows whether it is archived and where.

AutoArchive is not available in new Outlook. If you moved from classic to new Outlook, any archive.pst it created is still on disk but is not opened automatically. See below for opening a PST in new Outlook.

4. It is in the Online Archive, not the Archive folder

What you see: in a work or school Microsoft 365 account, mail older than about two years is gone from every normal folder.

There are two different things called “archive”. The Archive folder is where the Archive button moves mail; it is part of the mailbox. The Online Archive, called In-Place Archive in new Outlook and Outlook on the web, is a separate archive mailbox on the server. Microsoft’s online archive article warns readers to be “careful not to confuse” the two.

Exchange Online’s default retention policy includes a tag that moves items older than two years (730 days) to the archive mailbox, so mail can move there without anyone doing anything. Look for Online Archive or In-Place Archive in the folder list, and remember that classic Outlook’s search does not include it unless you change the search scope.

5. It was imported somewhere you did not expect

What you see: a PST import “worked”, but the mail is not where you looked.

The import wizard can put the PST’s folders inside the folder that was selected when you started (Microsoft’s import article describes “Import items into the current folder”), so a whole folder tree can end up under the Inbox or another subfolder. Expand every folder with Ctrl+6 (Folder List), and check the folder you had selected at the time. Duplicate handling can also skip items that already existed in the target.

6. Search is not looking in the right place

What you see: you know an email exists, but search does not find it.

Classic Outlook searches only the current mailbox by default. Microsoft’s PST article says other data files “won’t be searched unless you change your search scope to All Mailboxes.” Open PSTs and the Online Archive are easily missed this way.

If the scope is right and results are still incomplete, the Windows search index may be damaged. Microsoft’s steps to rebuild the search catalog go through Control Panel › Indexing Options › Advanced › Rebuild. Rebuilding takes hours on a large mailbox and the mail is not affected.

7. The PST is not open in this profile or this Outlook

What you see: whole folders that you had before are gone.

A PST appears in Outlook only while it is open in that profile. After a new computer, a new profile, or a move from classic to new Outlook, the file is still on disk but not shown. In classic Outlook use File › Open & Export › Open Outlook Data File. In new Outlook use Settings › Files › Outlook Data Files › Add file, but note Microsoft’s conditions: it requires classic Outlook installed on the same PC, a Microsoft 365 subscription, and does not work on Windows on ARM. Our guide to PST files in the new Outlook goes through them, and where is my PST file helps find the file.

8. The attachment is there but blocked or packed

What you see: the email has arrived but the attachment is missing, unopenable, or replaced by a file called winmail.dat or ATT00001.dat.

• Blocked file types. Outlook blocks attachments that can run code. Microsoft’s list of blocked attachments includes .exe and, perhaps surprisingly, .pst itself. The fix is on the sender’s side: a link to OneDrive or SharePoint, or a .zip file.
• winmail.dat. When Outlook sends in its rich text format, the attachments travel inside a winmail.dat that other mail apps cannot open. Microsoft’s article on TNEF explains the mechanism. The winmail.dat opener gets the files out in the browser.

9. It was deleted and can still be recovered

What you see: the mail is not in any folder or in search.

Check Deleted Items first. For Exchange and Microsoft 365 mailboxes, mail removed from Deleted Items goes to a hidden recoverable area for a period set by the organisation: in classic Outlook, open Deleted Items and choose Home › Recover Deleted Items From Server. Microsoft’s recovery article gives 30 days for Outlook on the web. Mail deleted from a PST has no such safety net; only a backup copy of the file helps.

10. A repair moved or removed it

What you see: after running SCANPST (the Inbox Repair Tool), folders are empty or items are missing.

SCANPST rebuilds the file’s structures, and Microsoft’s description of how it works is candid: if a damaged block “was part of a specific item in Outlook, the item will be removed”, and messages it cannot place go to a Lost and Found or Orphans folder. After a repair, open the folder list (Ctrl+6) and look for Recovered Personal Folders and Lost and Found. Microsoft notes the rebuilt default folders “are usually empty” and that “items that are missing from the Lost and Found folder may be beyond repair.”

SCANPST keeps a .bak copy of the original file next to it by default. Do not delete it until you are sure nothing else can be recovered.

11. An old PST hit its size limit

What you see: new mail stopped arriving in a PST at some point, AutoArchive stopped working, or moving items fails with “has reached its maximum size.”

PST files made by Outlook 2002 and earlier, and any later file deliberately created in the old format, use the ANSI format, which Microsoft’s size limit article caps at 2 GB “to prevent corruption.” When a file reaches its limit, items cannot be copied or moved into it, and if it is the archive file, “the Auto-Archive operation fails.” Mail that was never added is not in the file. The current format allows 50 GB by default. Our guide to a PST file that is too large covers both.

12. The file is damaged

If none of the above explains it, and Outlook reports errors such as “The file is not an Outlook data file” or “cannot be accessed”, the file itself may be damaged. Stop using it, make a copy before trying anything, and read what to do before you try to repair a PST.

Look at the file without Outlook in the way

Most of the causes above are about how Outlook shows a file: download windows, views, filters, search scopes, which files are open. Opening the PST outside Outlook removes all of them and shows what is actually stored.

The PST Viewer does that in the browser, without Outlook and without uploading the file. It lists every folder with the number of messages the file says it holds, including folders such as Lost and Found, so you can see straight away whether the missing mail is in the file. For an OST (the local copy of a mailbox), OST to PST turns it into a PST that you can open anywhere. If the viewer cannot read the file, the free health check shows what is damaged without changing it.

Sources

• Microsoft Learn: Only a subset of your Exchange mailbox items is synchronized, How to repair a personal folder file, Configure size limit for PST and OST files (updated 10 September 2026), Default retention policy in Exchange Online, How TNEF affects email messages.
• Microsoft Support: Work offline in Outlook, Can’t find email after importing a PST, AutoArchive settings explained, Online archive mailboxes, Import from a PST, Open and find items in a PST, Rebuild the search catalog, Blocked attachments, Recover deleted items.