A MBOX file is similar to a PST file, in that it contains a collection of emails. PSTs will be familiar to those of us in the Windows world, as it’s one of the old formats Outlook will use.

(Side note: PSTs are bad, but they do function well as a way of transporting a large chunk of mail from one place to another).

MBOX is the Unix version of PSTs. Google also uses this for Gmail, so if you run an export job, you’ll end up with a MBOX file. Microsoft Outlook doesn’t support this format though – so if you’re sent one, how do you view the contents?

If you start Googling, you’ll come across a bunch of ‘free’ viewers and converters. Most of these are free in the demo sense, and will only view or covert 20ish emails.

I eventually found these two free solutions and tested that they worked; if you find any others feel free to share.

Windows Mbox Viewer

This is a free, open source viewer of MBOX files. There’s no installer, just launch the exe, open your MBOX file and you’ll get a simple list of emails and can view the contents. Beyond being able to do searches, the program doesn’t do anything else. This is a great, simple solution if you just want to view the contents of the MBOX file. If you have Outlook installed, double clicking on an email will open it in Outlook, which can then be saved/printed.

Thunderbird

This is also completely free, from Mozilla. Here is a great set of instructions on how to configure Thunderbird to be able to read your MBOX file, but there’s a few more steps involved. Once Thunderbird can see them, you have a lot more options. The emails can be synced to another mail server, or you can simply select emails and save them out. They’ll be saved in the EML format, which Outlook will then recognise. More information about importing and exporting is available here.

I never found completely free software to convert from MBOX to PST, so if you really need that functionality, it might be time to take out the credit card and pay a hard working developer!