What is an RSMF File?Chat Evidence

📖 What is an RSMF File?

An RSMF file is a container for chat evidence. RSMF stands for Relativity Short Message Format. The RSMF format holds normalized short message data, the kind that comes from phone texts, workplace chat rooms and mobile messaging apps, so legal review software can present a conversation as if it were a single document.

Relativity, a widely used eDiscovery platform, created the format in 2019. Before it, every chat app exported conversations in its own layout, which made review slow and inconsistent. RSMF gives all of that data one shared shape. A message from iMessage and a message from Bloomberg chat end up described the same way inside the file, so a reviewer sees a single consistent conversation view no matter where the chat started.

The extension is .rsmf. Under the surface the file is built on ordinary, open standards, which is what lets tools other than Relativity open it. That structure is the key to everything else on this page, so the sections below walk through what an RSMF file holds, how it is put together and how to open one.

⚡ Quick Facts

🗂️ What an RSMF File Holds

An RSMF file has three layers, one wrapped inside the next. Understanding these layers explains why a normal unzip tool can crack the file open but still cannot show you the conversation.

The outer layer is an email. The outer envelope obeys RFC 5322, the internet standard behind ordinary email. Among its headers, X-RSMF-Version is the one that matters: it marks the file as RSMF 1.0 or 2.0. Because of this envelope, people sometimes call an RSMF file an EML message in disguise.

The email's attachment is a zip archive named rsmf.zip, carried in the email as base64-encoded data. The archive uses standard DEFLATE compression and is never encrypted, so any zip tool can list what is inside it once decoded.

At the root of that archive sits the heart of the file: a manifest named rsmf_manifest.json. This JSON file is where the real chat data lives. Beside it in the archive are the attachment files and avatar images that the messages point to.

🔬 Inside the Manifest

The rsmf_manifest.json file is the part that matters most. It describes the whole conversation in structured data, and a viewer reads it to rebuild the chat on screen. The manifest has four main lists.

Version records the format version. Participants lists everyone in the conversation, each with an id, a display name and often an avatar. Conversations groups events by a conversation id. Events is the long list: every individual message, each tied to a participant, a conversation and a timestamp. A single event can also carry a parentid that links a reply to its parent, which is how a threaded reply in a tool like Slack keeps its place. RSMF 2.0 adds event collection ids for grouping related events.

Timestamps follow the ISO 8601 standard, for example 2010-02-18T10:05:11.0000000Z, so the time a message was sent is precise and consistent no matter which time zone the reviewer sits in.

// a simplified rsmf_manifest.json
{
  "version": "2.0",
  "participants": [
    { "id": "p1", "display": "Alex Morgan" },
    { "id": "p2", "display": "Sam Lee" }
  ],
  "conversations": [
    { "id": "c1", "participants": ["p1", "p2"] }
  ],
  "events": [
    {
      "id": "e1",
      "type": "message",
      "participant": "p1",
      "conversation": "c1",
      "timestamp": "2024-05-14T09:12:03Z",
      "body": "Did the report go out?"
    }
  ]
}

Any tool that reads this manifest can rebuild the conversation. That is exactly how a viewer other than Relativity is able to display an RSMF file.

📂 How to Open an RSMF File

There are three practical ways to open a .rsmf file, depending on what you have and what you need to see.

1. Relativity Short Message Viewer. If your organization runs Relativity or RelativityOne, the file is ingested into a workspace and the built-in Short Message Viewer renders the conversation with search, timeline and coding tools. This is the full review environment, and it needs a Relativity licence.

2. A free RSMF viewer for Windows. When an RSMF file arrives by email and you do not have a Relativity seat, a dedicated desktop viewer opens the file directly and shows the conversation as chat bubbles. Nothing is uploaded and no licence is involved. This is the quickest route for a law firm or examiner who only needs to read what is in the file.

3. A zip tool, for the raw parts only. Because the archive is a standard zip, you can rename the file and extract rsmf_manifest.json and the attachments. You will see the raw JSON and the attached files, but not a readable conversation. This is useful for a developer inspecting structure, not for review.

💬 Where RSMF Files Come From

Almost any data that looks like a conversation can become an RSMF file. The chat data can be pulled straight from an app through an API or handed over as an export file such as JSON or XML, then written into the format. Relativity can build RSMF directly for Slack and Microsoft Teams, its Collect tool can convert chat to RSMF automatically, and partners on the Relativity App Hub offer RSMF creation as a service.

More than 75 different chat applications have been converted to RSMF, and the list keeps growing because any platform with messaging can be supported. Typical origins run from phone messaging like SMS and Apple iMessage, through workplace tools like Microsoft Teams and Slack, to older instant messengers like Skype. Regulated finance chat such as Bloomberg and mobile-collected WhatsApp threads are common too.

Forensic suites play a large role here. A tool such as Cellebrite can export a per-custodian chat extraction straight to RSMF, which is then handed to the legal team for review. Because the format is open, in-house scripts and third-party collection apps can build RSMF files too.

⚖️ RSMF 1.0 vs RSMF 2.0

The format ships in two revisions. RSMF 2.0 came later to record more of what modern chat apps track. Both are valid, and the X-RSMF-Version header tells a viewer which one it is reading. RSMF 2.0 is generally preferred because it carries richer data.

🔓 An Open Format with a Published Schema

A common misunderstanding about the RSMF format is that it is locked and proprietary. It is not. The format is an open container backed by a published schema. That openness is exactly why forensic suites, processing vendors and in-house scripts can all produce valid files without touching Relativity.

Relativity even provides an open-source RSMF validator and the schema on GitHub, so a builder can check that a file it created is correct before handing it over. The validator confirms the manifest matches the schema and that attachments are cross-referenced correctly between the manifest and the zip.

What is closed is the reading experience inside Relativity. The individual message metadata in the manifest is not searchable or visible outside Relativity's own Short Message Viewer. That is a review-tool boundary, not a limit of the file format itself, and it is why a separate viewer is useful when you only hold the file.

📧 RSMF vs EML

Because an RSMF file is built on the email standard, people often ask how it differs from a plain EML email file. The wrapper is the same. The payload is not.

An EML file is a single email message: one sender, some recipients, a subject, a body and attachments. An RSMF file uses that same envelope but fills it with a structured record of an entire chat, many messages between many participants, described in the JSON manifest rather than written out as email text.

So every RSMF file is technically an email file, but not every email file is an RSMF file. If you rename a .rsmf file to .eml and open it in an email client, you will see the wrapper and the zip attachment, not the conversation. Reading the conversation needs a tool that understands the manifest inside.

🛡️ Is It Safe to Open?

An RSMF file is data, not a program. It does not run code when you open it, so the file itself carries no direct risk the way an executable does. The care needed is about the contents, not the format.

RSMF files usually hold legal evidence, which means the real concerns are confidentiality and chain of custody. Open the file with a read-only viewer so the evidence is never altered, and prefer a tool that works offline so the conversation never leaves your machine. Uploading legal evidence to an online converter is the risk to avoid.

Attachments inside the file, such as images or documents, are ordinary files and should be treated with the same caution as any attachment from an outside source.

🛠️ Common Issues

🏛️ A Short History

Chat evidence became a real problem for legal teams as work moved off email and onto messaging apps. A single case might involve Slack, Teams, iMessage and WhatsApp, each exporting data in its own shape. Reviewers needed one consistent way to look at all of it.

Relativity introduced RSMF in 2019 to solve exactly that. By wrapping normalized chat data in a familiar email structure, the format let existing review workflows treat a conversation like a document. RSMF 2.0 followed to capture newer chat features such as read receipts, message direction and history events, keeping pace with how modern messaging apps actually work.

Today RSMF is a common delivery format for chat evidence across the eDiscovery industry, produced by forensic tools and processing vendors well beyond Relativity itself.

❓ Frequently Asked Questions

📝 Summary

An RSMF file, extension .rsmf, is Relativity Short Message Format: a container that packages chat evidence for legal review. Structurally it nests three standards: an email envelope on the outside, a zip archive as the email attachment, and a JSON manifest at the root of that zip that describes every participant, conversation and message alongside the attached files.

The format is open, with a published schema and an open-source validator, so tools beyond Relativity can build and read RSMF files. What is closed is the reading experience inside Relativity's own viewer, which is why a free RSMF viewer earns its place the moment someone emails you a .rsmf file and you need to read the exchange without a Relativity seat.