Fix No Valid MBOX Files Were Found Import Error in Apple Mail

Experiencing No Valid MBOX Files Were Found error when trying to import MBOX files in Apple Mail? There are several possible reasons why Mail fails to import. Here, we have presented all the tested troubleshooting steps so that you can easily migrate to Apple Mail or restore archived emails error-free.

What Does “No Valid MBOX Files Were Found” Mean?

MBOX can exist with or without an extension, and is a commonly used email file format storing emails and attachments, and is in a proper folder structure used for archiving and migrating mailboxes.

However, when importing MBOX files in Apple Mail, the Mail app needs to validate the mailbox structure and content inside the MBOX files. When the application fails to authenticate, it returns the MBOX file not recognized by Apple Mail error.

Common Causes for the MBOX File Not Being Recognized by Apple Mail Error

There are several reasons why No Valid MBOX Data Files Were Found might pop up:

• MBOX got corrupted during transfer or at the time of export
• User has selected the wrong folder
• An incorrect MBOX directory level was selected from the folder-structure from exported from other email clients or Apple Mail
• The selected MBOX is empty – there is no data to import
• Different MBOX structure from older Mac OS versions or other email clients

Troubleshooting Solutions to Fix No Valid MBOX Files Were Found

These steps are applied to all MBOX files, most Mac Mail versions, and macOS 10.6 to macOS 10.7.

Primary Steps before You Start Fixing the Error

These general fixes only help avoid the system cache or temporary issues caused by system glitches.

• Close and restart the Apple Mail email client.
• Restart your Mac OS in safe mode.
• The desired MBOX files you want to import must actually be present inside the selected folder.

However, first assure the .mbox file or folder is undamaged and properly formatted before attempting any of the fixes. Here is how to verify:

• Right-click on the folder >> Select Properties >> Check if the Type of File is MBOX.
• Open MBOX with Notepad or any other text editor. The image below shows what the general MBOX structure looks like in Notepad. If the content consists of arbitrary characters, it’s likely your MBOX is not valid.
  
• Check the folder size; if 0 Kb, the folder is empty and thus returns a No Valid MBOX Files Were Found.

Fix 2: Select the correct MBOX from the Folder Structure

The image displays how emails are stored in MBOX files or folders. Selecting the correct file or folder helps you get rid of No Valid MBOX Files Were Found error when importing.

MailBackup
│
├── Inbox.mbox – CAN BE SELECTED
│             └── Contents – DO NOT SELECT
│             └── Resources – DO NOT SELECT
│             └── Data – DO NOT SELECT
│             └── mbox – DO NOT SELECT
│
├── Sent.mbox – CAN BE SELECTED
│             └── Contents – DO NOT SELECT
│             └── Resources – DO NOT SELECT
│             └── Data – DO NOT SELECT
│             └── mbox – DO NOT SELECT
│
└── Drafts.mbox – CAN BE SELECTED
            └── Contents – DO NOT SELECT
            └── Resources – DO NOT SELECT
            └── Data – DO NOT SELECT
            └── mbox – DO NOT SELECT

• You can either select the whole folder with the backed-up MBOX or the subfolder MBOX, like Inbox.mbox, Sent.mbox or Draft.mbox.
• Do not select the internal MBOX to avoid the No Valid Mailbox Detected Error in Apple Mail.

Fix 3: Provide Required Permissions to MBOX File/Folder

1. In the Finder, right-click.
2. Select Get Info or press Cmd+I.
3. Unlock the Lock icon at the bottom and enter the password to unlock.
4. In the Get Info window, scroll to Sharing & Permissions.
5. Ensure it is selected to Read & Write.
6. Apply changes and save.

Fix: No Valid MBOX Files Were Found when Importing Apple Mail Data

You can also encounter the error when importing data from Apple Mail as the source.

Older Apple Mail stores email data in a different MBOX structure. Here is how to avoid the error when importing:

1. Close the Mail Application.
2. Go to ~/Library/Mail/(older version)/MailData/MessageRules.plist.
3. Copy the file.
4. Paste it in the
5. Open Mail App on Mac.
6. Paste it inside the ~/Library/Mail/(new version)/MailData/
7. Click on File >> Import Mailboxes.
8. Choose the mailbox folder (~/Library/Mail/).
9. Press Continue to start the process.

Additional Tip

Preventive Measures to Avoid No Valid MBOX Files Were Found

• Do not close the email client when creating an export.
• Ensure you split MBOX files; larger files can also result in No Valid MBOX Found error.
• Content in the MBOX in folder structure is interlinked; thus, do not rename MBOX mailboxes.
• Avoid compressing or zipping folders, as Apple Mail only takes the raw message format.