About Email Formats

Modified on Thu, 7 Aug at 12:42 PM

About Email Formats | .pst vs .msg vs .eml vs .mbox vs .mht

Understanding the difference between email file formats is key to ensuring successful processing, accurate review, and useful productions in Nuix Neo Discover. This article explains common formats and why we often prefer to process into .mht over .msg during ingestion.

PST: Outlook Mailbox Archive

.pst (Personal Storage Table) is a complete Outlook mailbox export.
Includes folders, messages, calendars, and attachments.
Often used for full custodial collections.
Must be processed to extract individual emails into reviewable format.

MSG: Individual Outlook Email

.msg files represent a single email message saved from Outlook.
They preserve metadata and attachments—but with important limitations.

⚠️ Note: If .msg files are loaded into Nuix, embedded attachments are not always retained in the native view. If you export or review the .msg native, there may be no visible indication that an attachment ever existed—posing risk during privilege or responsiveness review.

Also, .msg files are dynamic: fields like "Date Modified" can change each time a .msg file is opened, which may impact defensibility and chain of custody. In some cases, viewing the native file in Outlook can even trigger an attempt to send the email to its original recipients. Additionally, .msg files require Outlook to view, while .mht files can be safely opened in a browser or text reader.

For this reason, we process into .mht by default in Nuix.

MHT: Web Archive of Email (Preferred Native Format)

.mht (MHTML) is a web archive format capturing the full visual layout of an email, including embedded attachments.
Nuix Neo Discover displays MHT files reliably and ensures reviewers can see attachments—even if only referenced inline.
Static and tamper-resistant once generated—unlike .msg.
Recommended for native email rendering and exporting in most review workflows.

EML: Individual Email (Generic Format)

.eml files are similar to .msg but more widely supported outside of Outlook (used by Gmail, Apple Mail, Thunderbird).
Can include attachments and metadata, but may behave differently depending on the export method.
Often produced when converting .mbox mailboxes.

MBOX: Mailbox Format Used Outside Outlook

.mbox is used by Gmail Takeout, Apple Mail, and others to store full mailboxes.
Contains multiple messages and must be converted to .eml or .pst for review purposes.
Does not support Outlook-specific features or metadata.

Quick Comparison Table

Format	Type	Common Use	Notes
`.pst`	Mailbox	Outlook	Best for full mailbox exports. The user can choose what to export. Doesn't have to be everything. It's done on a folder-by-folder basis.
`.msg`	Single email	Outlook	Dynamic; embedded attachments may not show in native view
`.mht`	Email archive	Processed native format	Preferred for review in Nuix; captures attachments and layout
`.eml`	Single email	Apple Mail, Gmail	Good compatibility; behavior varies slightly from .msg
`.mbox`	Mailbox	Gmail, Apple Mail	Requires conversion; lacks Outlook metadata

Platform-Specific Notes

Microsoft Outlook

Uses .pst and .msg formats.
Full-featured, but .msg has limitations for defensible review.

Gmail (via Google Takeout)

Exports as .mbox files.
May need conversion/processing to .eml or .pst before use, which can be done in Nuix.

Apple Mail

Uses .mbox or folder of .eml files.
Attachments usually preserved, but formatting can vary.

Have questions about your email exports or need help converting formats? Send us a message!