What Is an MSG File?

A .msg file holds one Outlook email that you can keep or share. It can contain the message’s sender, recipients, subject, dates, formatting, and attachments. Outlook uses a Microsoft-developed format to store that information.

Save an email as .msg when you need to keep it as an Outlook item. A compatible version of Outlook opens it most easily. Other email programs may not read all of its contents.

What a MSG file contains #

A .msg file stores one Outlook item, such as an email, as a separate file from the main mailbox. It uses Microsoft’s compound binary format, a file format that stores message details and other content in a structured way. The format is proprietary, although its structure has been documented.

ContactMonkey’s instructions for saving email files say that the file preserves email details such as headers, formatting, and attachments. Saving a message as .msg keeps it as a single Outlook message, separate from other messages in a mailbox archive.

MSG and EML are different formats #

An .eml file is a widely supported email format based on the MIME standard. MIME is a standard for formatting email content. A .msg file uses Outlook’s format, so programs outside Outlook may handle it differently. Both formats can preserve message content and attachments, but they are not interchangeable.

Renaming a .msg file to .eml does not change its format. A user report in a Microsoft Q&A discussion describes the renamed file failing to display the message. Use an email conversion tool if you need a different format, and check the resulting file to confirm that its message details and attachments remain intact.

How to open an MSG file #

In Windows, Microsoft says you can open a .msg file in new Outlook by right-clicking it, selecting Open with, and choosing Outlook (new). You can also drag supported message files onto the reading pane in new Outlook or Outlook on the web. Microsoft states that opening .msg and .oft files in those versions requires a qualifying Microsoft 365 subscription.

If double-clicking the file does not open Outlook, Windows may have another program set as the default for .msg files. Choose Outlook through Open with, or update the default program in Windows settings. Outlook versions handle .msg files differently. Users have reported problems opening them in new Outlook for Mac in a Microsoft Q&A thread.

Handle MSG files with care #

An .msg file can include attachments, so treat one from an unfamiliar sender as you would any unexpected email attachment. A SANS Internet Storm Center analysis of one submitted .msg file found a malicious archive attachment containing an executable. That finding applies to the file in the analysis. Scan unexpected files and avoid opening suspicious attachments.

Save the original email as received when keeping it as a record; forwarding it first can alter its structure. ContactMonkey support article warns that a forwarded copy may be empty or fail to open.

$ curl -fsSL https://raw.githubusercontent.com/vincentsch/mailmd/main/install.sh | sh

Set up mailmd so you can read my email. Use https://github.com/vincentsch/mailmd: read its AGENTS.md and follow the steps. Connect my mailbox and run the first sync. Then show me where the files are.