How to fix “no valid MBOX files were found” on import
This means the import tool was pointed at the wrong thing, usually a single file or the wrong folder level, instead of the parent folder that holds the MBOX files. Jump to your situation below or work through the methods in order.
By Neeraj Singh ~5 min Updated Jun 2026 91% found this helpful
Error message
No valid MBOX files were found in the selected location.
Summary
Both Thunderbird's ImportExportTools NG and Apple Mail show a version of no valid MBOX files found when you point the import at the wrong level. These tools expect you to select the parent folder that contains the MBOX files, and they scan inside it; if you select a single file, an empty folder, or the wrong level of a nested structure, they find nothing to import. Apple Mail in particular expects a specific .mbox package structure, not a lone file. The fix is to point the import at the correct folder, confirm the files are genuine MBOX (plain text starting with a From line, not renamed PST or EML), and flatten or correct the folder structure if it is nested. Once the tool is aimed at the right folder, the import proceeds.
What this error means
MBOX import tools are built to process a folder of mailboxes, not one file at a time. They open the folder you choose and look for MBOX files inside it. So when the message says none were found, it almost always means you selected the wrong thing to import, not that your mail is missing.
Apple Mail adds a twist: it stores each mailbox as a .mbox package, a special folder, and its import expects that structure rather than a bare file. Pointing either tool at the correct parent folder, with valid MBOX files inside, resolves the error.
Common causes
A single file was selected instead of the parent folder.
The wrong level of a nested folder structure was chosen.
Apple Mail was not given its expected .mbox package structure.
The selected folder is empty or has no MBOX files.
The files are not real MBOX (renamed PST, EML or other format).
The MBOX files have an unusual extension the tool does not recognise.
Expert insight
“This is almost never a broken file, it is aiming the import at the wrong spot. The tools want the folder that contains the mailboxes, and they look inside it, so if you hand them a single file or the wrong level they shrug and say nothing here. Apple Mail is the fussiest, it wants its .mbox package structure, not a loose file. Point the import at the parent folder with the real MBOX files inside, and it springs to life.”
Manager, Tech Support & Operations · 19+ years fixing Windows and system errors
✓ How to fix it
Method 1
Select the parent folder
1In ImportExportTools NG, choose to import an mbox file directory and select the folder that contains your MBOX files, not a single file.
2The tool scans inside that folder for mailboxes.
3If you only need one mailbox, put that MBOX file in its own folder and select that folder.
Method 2
Use the right structure in Apple Mail
1Apple Mail expects a .mbox package, not a bare file.
2In Mail, File, Import Mailboxes, choose Files in mbox format, then select the folder one level above your .mbox items.
3Do not select the .mbox file itself.
Method 3
Fix a nested structure
1If your export has nested subfolders, point the import at the level that directly contains the MBOX files.
2Flatten deeply nested folders if the tool will not recurse into them.
3Re-run the import.
Method 4
Confirm the files are real MBOX
1Open a file in a text editor, a real MBOX starts with a line beginning From followed by message headers.
2If it is a renamed PST, EML or other format, convert it to MBOX first.
3Then import the genuine MBOX files.
This is a selection problem, not a corruption problem, so the fix is to aim the import correctly: choose the parent folder that contains the MBOX files, not a single file. Apple Mail is the strict one, it needs its .mbox package structure, so select the level above the .mbox items, never the file itself.
Frequently asked questions
Why does it say no valid MBOX files were found?
Because the import was pointed at the wrong level, usually a single file or an empty or wrong folder, instead of the parent folder that contains the MBOX files.
How do I import MBOX into Thunderbird correctly?
Use ImportExportTools NG, choose to import an mbox file directory, and select the folder that contains your MBOX files. The tool scans inside it for mailboxes.
How do I import into Apple Mail?
In Mail choose File, Import Mailboxes, Files in mbox format, then select the folder one level above your .mbox items. Apple Mail expects its .mbox package structure, not a bare file.
How do I know if a file is really MBOX?
Open it in a text editor. A real MBOX begins with a line starting with From followed by message headers. A renamed PST or EML is not valid MBOX and must be converted first.
My folders are nested, what do I do?
Point the import at the level that directly contains the MBOX files, and flatten deeply nested folders if the tool will not recurse into them.
Do I select the .mbox file or the folder?
The folder. Both Thunderbird and Apple Mail want the parent folder that contains the MBOX files or .mbox packages, never the individual file.
Still not working?
If the tool still finds nothing with the right folder selected, the files may have a non-standard extension or a hidden character in the name that the importer skips. Rename a test file to a clean name ending in .mbox in its own folder and import just that to confirm. You can also submit your error to us for a tailored fix.
