How to split large mail Mbox files in Windows 10

So, a friend of mine changed his email provider and he decided to backup the old emails into one large 237MB mbox file. The problem was that the email app didn’t allowed restore from mbox files larger than 50MB. This was a mess, especially since he really needed to access the an email from 2 years ago. He asked me for a solution and here’s what I found.

There are few php scripts that allows you to split the file, but since I had only a Windows laptop, that was out of the question. I also found a Mbox split app that sould do the job, but unfortunately the mbox splitting function was not available for the demo version. As my patience was coming to an end, I discovered a freeware mbox splitting app that did the job. Well, sort of. It was not a one-click job, I needed to use CMD, but I’ve manage to split the large mbox file into smaller files and I have restored the email account completely. Here are all the steps:

  1. Head over to and download eml2mbx 0.65 and mbx2eml 0.68
  2. Unpack mbx2eml 0.68 and follow the instructions found in mbx2eml_step_by_step.txt file located in archive in order to split the original Mbox file into smaller EML files. They are pretty simple
  3. The output result will be a folder that contains all the emails. Now, you need to split that folder into two or more, depending on your need. For example, let’s say you have an initial Mbox file that has 86 MB and you are allowed to upload maximum 50 MB per file. The output EML folder will have around 90 MB. You should move half of the files in other folder. Now, I you’ll have two EML folders with 45MB each. It’s time to pack them back to MBox format.
  4. Unpack eml2mbx 0.65 and follow the instructions found in eml2mbx_step_by_step.txt file located in archive in order to convert each of the two folders from step 3 into Mbox files.
  5. You can restore your mail from the resulted Mbox files.

The operation of splitting one Mbox file into multiple files could be a bit tricky, especially if you decide to use this technique. Since everything is done from the command line, you should make sure that you write each command and folder name correctly. That’s the trick! In the future, maybe we’ll find an app that does the job for you automatically… but until then, this is the solution we recommend. Do you know other free apps that split Mbox files? Let us know in the comment section below.

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