6 Email eDiscovery File Types (Must Know): PST, MSG, EDB, OST, EML & MBOX

03 September 2019 by Anith Mathai eDiscovery email file-type msg pst edb ost eml mbox
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Takeaway: There are 6 eDiscovery file formats you’ll regularly come across: MSG, PST, EDB, OST, EML, and MBOX. So, make sure your eDiscovery software can handle all of them.

Handling eDiscovery email is easy when you have the right software.

Just drag-and-drop your files into your eDiscovery browser. They’ll be processed and deduplicated in seconds. And you’ll be able to search your case, tag files, redact privileged information, and produce documents in different formats.

Still, it’s worth knowing the different email file types you’ll come across.

And there are 6 of them. You can Google search file types for detailed information on each, but here’s a quick comparison for ease.

Email file types in the Microsoft Outlook universe

Outlook is one of the most popular desktop email clients out there. Which is why you’ll deal largely with these 4 Outlook email file types.

1. MSG files: How Outlook stores a single email

An MSG file is one with a ‘.msg’ file extension. And Microsoft’s email client Outlook uses the MSG format to store single email messages. When you drag-and-drop an email from Outlook to a folder on your computer, the email message is converted into an MSG file. This file stores the email text, but it also stores the email metadata – things like who sent the email, who received it and when, etc. And it also stores links and attachments from the email. Microsoft owns the MSG file format, though. So, you have to open MSGs with Outlook. Or with Microsoft-compatible software.

2. PST files: How Outlook stores groups of email

Outlook converts single emails into MSGs when you move them out of your mailbox. But it stores your mailbox (i.e., all you emails) as a single PST file – a file with a ‘.pst’ extension. Have you wondered “what does PST stand for?” PST stands for Personal Storage Table. And PSTs are a great way to organize, store, and share batches of email. For example, you can put all your emails from last year into a PST file, and ‘archive’ that PST. And you can have multiple PSTs (e.g., one for each year of the last decade) open at the same time, as well as your main, active PST. For eDiscovery, you can even load emails from different custodians into a single PST file. And you can store these PSTs on local hard drives, a USB drive, or in the Cloud. Also, as you move PSTs around, their metadata might change. But the metadata of the emails inside stays untouched. (Learn more about PSTs.)

3. EDB files: How Microsoft stores PSTs on its Exchange Server

Microsoft Outlook is an email application that sits on your computer. But Outlook is communicating with a much more powerful, back-end server application: Microsoft’s Exchange Server. It’s the Exchange Server that stores your emails (along with your calendars, tasks, etc.). And Outlook syncs with it. The Exchange Server stores thousands of PSTs together as EDB files (I.e., files with a ‘.edb’ extension) – ‘EDB’ standing for Exchange Database. Typically, forensic ESI (electronically stored information) specialists deal with EDBs. For example, they’ll contact a client’s IT department for PST files of particular custodians.

4. OST files: How Outlook stores groups of email, offline

As we’ve seen, Outlook syncs your PSTs with the Exchange Server. But what if you don’t have an internet connection? Well, Outlook stores your data as an Offline Storage Table (OST). And when you get back online, it syncs the OST with its corresponding PST. This can get tricky with eDiscovery, though. Because if an OST hasn’t been synced, you’ll miss out on potentially important data.

Email file types outside the Microsoft Outlook Universe

These are the open-source, text-based file types.

5. EML files: Single emails you can open without Outlook

Files with the ‘.eml’ (i.e., ‘email’) extension are similar to MSGs, in that they represent single emails. But MSG files use a special Microsoft message format. So you need Outlook to open them. EMLs, in contrast, are stored as plain text files. In the .eml vs .msg comparison, the advantage of the EML file format is that you can open EML files with many other email applications – e.g., Mozilla Thunderbird and Outlook Express (the free, stripped-down version of Outlook). This gives you so many more options. In addition, you can also convert MSGs into the EML format, using free or paid applications and websites. The aim of the EML format was to make it more accessible. Microsoft even tried streamlining viewing emails by providing previews of EML files directly in Explorer windows without needing to open a dedicated Microsoft eml viewer software. Unfortunately, this still required the installation of the Windows Live Mail software, which has since been retired.

6. MBOX files: Groups of emails you can open without Outlook Files with the ‘.mbox’ (i.e., ‘mailbox’) extension are like PSTs, but with some differences. For one, you can open them on non-Microsoft applications like Apple Mail and Mozilla Thunderbird. Also, unlike PSTs, an MBOX is a text file. So you can open it with text editors like Microsoft Word and Notepad. It stores all your emails, in sequence – with a separating line between each of them.

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