How to Split MBOX File into Smaller Files? 2 Best Methods

Published By Jamie Kaler

Approved By Rollins Duke

Published On December 24th, 2025

Reading Time 7 Min Read

Overview: Do you have a large size of MBOX files, and do you want to split MBOX file into smaller files? If so, then read this article. Here you will get a simple and easy-to-use solution to divide the MBOX file into small parts. Read more to know more.

The oversized MBOX files and their consequences seriously affect millions of users. Large-sized MBOX files lead to various issues, especially programming crashes, lagging for a long time on loading mailbox items, hardware failure issues while sharing such large files, etc.

MBOX files are obtained from a large number of email clients and services. Some of them are Apple Mail, Webmail, PocoMail, Google Takeout, PostBox, Entourage, Eudora, Opera, Netscape, Thunderbird, Spicebird, etc. Some use the original version of the MBOX file while others use an extended or modified edition of the mailbox file.

This article describes three manual & free ways to split MBOX file into smaller files or separate files. There is also an expert’s expert-recommended MBOX Splitter Wizard, which enables users to divide MBOX files into separate files based on Date, Size, or From the User fields. It also allows splitting MBOX files for emails between two dates.

Oversized MBOX File – Common Failure Issues

In MBOX Files, all the email content and related information are saved in a single text file. All the emails and messages are saved in a serial order, one after another. Each message is separated with the ‘From’ keyword while it terminates with a blank line.

An email conversation is a continuous process. A user may receive several emails regularly. Hence, the size of the mailbox file attached to it is also increasing. It results in various causes of working with MBOX files, like an error in opening MBOX files, incompatibility with the platform, etc.

The major issue that is faced by the users is the corruption of MBOX files. Large MBOX files are also seen to be causing abnormal behaviour in some mail clients, which requires split MBOX file. As though there is no file size limitation imposed by the new Thunderbird editions for saving emails on MBOX file at present time. But older Thunderbird versions support MBOX files only up to 4 GB.

Major Advantages of Splitting MBOX Files Are:

Share only the required emails with your seniors or colleagues instead of the whole mailbox.
As large MBOX files give more chances to become corrupt, splitting them ensures data security.
The corresponding email client hangs for a long time and consumes more time. Hence, loading only a few mailbox items will certainly reduce the time in loading mailbox items.

How to Split MBOX File into Smaller Files Manually?

First of all, open your Thunderbird on your system.
Now, click on the “Tools” menu from the top.
Now, choose the “ImportExportTools” and then click on “Import MBOX Files” options.
After that, choose the “Import One or More Files” option and locate the file.
After choosing the file, click on the “Open” button icon.

Now, after uploading the data file, we will export all folders one by one as a MBOX file.

Now, locate your MBOX file and open it.
Select the folders and right-click on them.
Now, choose the “ImportExportTools” option and then click on “Export Folder” option.
Lastly, choose the destination to save your final data safely.

Some Major Setbacks of this Manual Method

You can not split multiple MBOX files in bulk at the same time.
This method does not allow you to split corrupted and damaged files.
You need to follow the same steps multiple times for each file to split and export them.
Required to install the Mozilla Thunderbird installation on your system.

Which MBOX Splitter Wizard Will be Best to Split MBOX File?

Only RecoveryTools MBOX File Splitter Tool is the right offline and portable solution to split MBOX file into smaller files without cutting any information and details. It can divide your mailbox file by Date, into individual messages by User ID (from), or based on size. It allows splitting all types of MBOX files, including Thunderbird, Google Takeout, etc.

Download this amazing MBOX Splitter Tool from link given below:

Download Now Purchase Now

Note: The software will allow splitting only the first 25 emails to a new file during the trial version. The working of the utility is very simple. It also displays the preview of the emails in its working panel. One can analyse its working with the help of its working screenshot.

Complete Working Steps to Split MBOX into Separate Files

Download and install the then solution on your system.
Click on the “Open” button and choose between the “Select Files” and the “Select Folders” button to upload your single or multiple files.
After uploading your complete data, all the folders and subfolders will appear on the screen, so that users can analyze their data without wasting their time.
One can easily change or choose splitter options according to your requirements.
Start the process by clicking on the “Next” button to split MBOX file into smaller files.

Why MBOX File Splitter Tool Over Manual Methods?

This MBOX splitter tool provides dual options to upload your single and multiple MBOX files and folders to the panel as per your requirements.
Also, it supports all types of MBOX files exported from any email client, including Thunderbird, Google Takeout, Opera Mail, SeaMonkey, Horde Mail, Apple Mail, etc.
This MBOX splitter wizard maintains all the folder hierarchy and email components, including Bcc, Cc, To, From, Subject, Date, Formatting, Font Size & Colour, sender and receiver information, etc.
Users can use the advanced search option with multiple filters to find any particular and required email, which they want to analyze, and to split MBOX file into smaller files.
After uploading your complete data, users can analyze all the folders and subfolders on the panel including email body and header details.

Frequently Asked Questions

Ques: How can I open MBOX files for free?
Ans: Yes, you can open MBOX files for free using the RecoveryTools MBOX Viewer tool.

Ques: What is MBOX storage?
Ans: MBOX is a file format to store an email detail including the email header and body details of a folder. It is used by multiple email clients like Thunderbird, Apple Mail, Opera Mail, SeaMonkey, etc.

Ques: I have 1000+ MBX files, which I want to split to save my storage space. Does this software support MBX files?
Ans: Yes, our MBOX splitter tool supports all types of MBOX versions including MBX, MBS, etc.

Ques: I want to convert the MBOX file into an Outlook data file, is this tool saved in it?
Ans: For MBOX to PST conversion, you should use one of the best and most advanced MBOX converter tools for Mac & Windows.

The Verge

A large number of email clients are responsible for creating MBOX files. With time, the emails are continuously received and sent by the user, hence increasing the size of the MBOX file rapidly. But as it led to various issues, most of the users decided to split MBOX file into smaller files.

This article successfully describes the whole scenario of oversized MBOX files and how to manage them. It solves various queries of the users like ‘how can I split large MBOX files, how to break MBOX files into smaller parts, how can I split MBOX by date’, etc, using the MBOX splitter tool. If you still want to clear your doubts or wants to know more about this or any other topic, you can get in touch with out Technical Support team any time.