How to Import MBOX to Gmail (With & Without Thunderbird)

Prepare the source mailbox and Gmail account. MBOX files can come from several applications and services, including Mozilla Thunderbird, Apple Mail and Google Takeout.

First, identify exactly which MBOX file or files you need to migrate. If the mailbox contains multiple folders, keep the files organised so that you can identify Inbox, Sent, Drafts and other folders during the migration.

Also check the size of your MBOX files and the available storage in the destination Google account. Large mailboxes can take considerably longer to upload, because every message has to be processed and transferred.

If preserving folder organisation is important, decide how you want those folders to appear in Gmail account. Gmail uses labels rather than traditional folders, so imported folders may appear as labels depending on the migration method. It is also recommended to test the process with a small MBOX file first. This helps you confirm that messages, attachments, dates and folder organisation are being transferred as expected.

Method 1: Import MBOX to Gmail With Thunderbird

Thunderbird is a free way to import MBOX files into Gmail using IMAP syncing feature. However, it involves various steps, such as that; first you need to set up your Gmail account in Thunderbird using IMAP, then you import the MBOX file into Thunderbird Local Folders using ImportExportTools NG and finally you can copy the imported messages to your Gmail mailboxes.

Step 1. First, download Thunderbird and install it on your computer and launch it.

Note: Thunderbird is available for Windows, macOS and Linux. The interface may look different depending on the version you are using.

Step 2. Click the Menu tab and select New Account.

Step 3. Then in New Account, choose Email from the options.

Step 4. In the Account Hub tab, provide your Full Name, email address and click the Continue button.

Step 5. In older versions of Thunderbird, you might find this option under:

Menu >> Account Settings >> Account Actions >> Add Mail Account.

Step 6. Thunderbird usually automatically detects server settings for Gmail. Keep IMAP selected because this allows Thunderbird to sync messages with your Gmail account. Click Continue.

Step 7. Once you added Gmail account details, Thunderbird will open a window to sign in to Google.

Step 8. Sign in to your Google Account and follow the instructions on your screen. When Google asks for permission to access your account, review the permissions it is requesting and click Allow if you want to continue.

This is the authentication flow for Google OAuth 2.0. Most modern Gmail accounts use OAuth, instead of letting applications connect with a normal Gmail username and password.

Step 9. When authentication is complete and your Gmail account is added, click Finish to continue.

Step 10. Now, in Thunderbird’s left navigation panel, you will see your Gmail account and folders.

Step 11. Next, in Thunderbird Mail, click the menu bar and choose the Add-ons & Themes option and install the ImportExportTools NG add-on.

Note: Make sure that your are using the latest version of ImportExportTools NG compatible with your Thunderbird installation.

Step 12. Now, create a local folder in Thunderbird and right-click on it.

Step 13. Then, choose ImportExportTools NG >> Import mbox Files >> Individual mbox Files option.

Step 14. Choose the MBOX file you need and click Open.

Step 15. Thunderbird will import the messages into the chosen local folder.

Step 16. Open the imported folder and check that the messages are displayed correctly.

Step 17. After that, press Ctrl+A (Windows) or Command+A (macOS) to select all messages.

Step 18. After selecting the messages, right-click and choose: Copy To >> Your Gmail account >> Folder destination.

Once the transfer is done, log in to Gmail in your browser and verify that the imported messages are present.

This completes the MBOX to Gmail import process. However, this is a lengthy and time-consuming process.

Method 2: Google Workspace – Google’s import-mailbox-to-gmail Script

Google maintains an open-source GitHub project called import-mailbox-to-gmail that allows Google Workspace administrators to import MBOX files in bulk into users mailboxes. It is particularly useful when an organisation needs to migrate MBOX files for multiple users.

The project uses the Gmail API and a service account with domain-wide delegation. Once the service account is authorised, the administrator can organise MBOX files by user and run the migration from the command line.

Steps to use the Google MBOX import script

1. Download the import-mailbox-to-gmail script from the Google GitHub repository.
2. Create a Google Cloud service account and enable the Gmail API.
3. Download the service-account JSON credentials.
4. Create a main directory and create a separate folder for each Google Workspace user. Organize your MBOX files in:
   C:\mbox\user@example.com\

5. Open Command Prompt.
6. Run the scripts with the service account JSON file and MBOX directory:
   python import-mailbox-to-gmail.py --json Credentials.json --dir C:\mbox
7. The scripts import the MBOX files into the specified user mailboxes. Check Gmail and the generated log file for the import status.

This is how you can upload MBOX files using the import-mailbox-to-gmail scripts.

Note: Google project documentation recommends testing the migration with the test user before importing mail into actual user account. This helps identify authentication formatting or mailbox-related problems before a large migration. This approach is useful for administrators, but requires more setup.

Method 3: Import MBOX to Gmail Without Thunderbird

If you do not want to install Thunderbird or command line scripts, try Advik MBOX Converter for Windows PC. With this tool, you can migrate MBOX to Gmail in just a few simple clicks. Just run the tool, add .mbox files, choose Gmail as a saving option, enter Gmail account login credentials and press Convert to begin the importing process.

The software can import MBOX files to Gmail in bulk. Also, it offers advanced email filter options to upload selected emails from MBOX file based on date range, to, from, subject, etc. It preserves data integrity and folder structure while importing.

A free trial is also available to migrate 25 emails per folder. Download the tool today and try it for FREE.

Click the link button and download the free version to check its working steps.

   

Steps to Upload MBOX to Gmail

Step 1. Run the software on your Windows PC.

Step 2. Click the Select Files or Select Folders option to add .mbox files.

Step 3. Select the email folder you want to import.

Step 4. Choose Gmail as the target source from the list of various options.

Step 5. Enter your Gmail account login details and click Convert.

Step 6. The software will start uploading MBOX emails into Gmail account.

Once the process is completed, open your Gmail account and check the mailbox list. You will see a new folder with your .mbox file emails.

Watch How to Import MBOX File to Gmail Without Thunderbird

Gmail Limits to Know

Before starting a large MBOX migration, keep a few Gmail-related limitations in mind.

1. Gmail Storage

Your Gmail mailbox uses your Gmail account storage. A large MBOX migration can consume considerable space, especially when the source contains years of emails and attachments. Check available storage before starting the import.

2. Attachment Size

For personnel Gmail account, Google currently lists a 25MB attachment limit for messages. Google Workspace limits can differ because administrators control sending and receiving attachment limits.

This does not mean an MBOX file itself must be smaller than 25MB. The limit applies to email attachments, while an MBOX file is a mailbox container that can hold many messages.

3. Gmail Labels Instead of Traditional Folders

Gmail organizes messages using labels, rather than the traditional folder model. As a result, Thunderbird or MBOX folder may appear as a Gmail labels after migration.