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MSG is Microsoft Outlook's proprietary format based on OLE Compound Document (CFBF) binary structure. Each MSG file contains the complete email: sender, recipients, subject, date, message body (HTML, RTF, or plain text), embedded images, file attachments, and Outlook-specific metadata such as categories, follow-up flags, and reminders. Only Outlook or MSG-aware utilities can parse this format. You cannot open an MSG file in a text editor, a web browser, or a non-Microsoft email client.
EML is a plain-text format defined by RFC 5322. Each file stores one email message with MIME-encoded headers, body (HTML and plain-text alternatives), inline images, and file attachments. Open any .eml file in a text editor and you see human-readable From, To, Subject, and Date lines. Thunderbird, Apple Mail, Windows Mail, eM Client, Mailbird, and dozens of other clients read EML natively. One EML = one email = one portable, universally accessible file.
MSG locks your emails inside Microsoft's ecosystem. EML gives you universal access and long-term portability. If you leave Outlook, your .msg files become inaccessible without a converter. EML files remain readable on any platform, any operating system, and any email client for years to come.
Once converted, import the EML files into Thunderbird by dragging them into a folder in the mailbox panel. Apple Mail, eM Client, and Windows Mail also accept EML files directly — copy them to the client's storage directory or use the built-in import function.
MailConverter.exe "C:\Emails\*.msg" -sEML "C:\Output\EML\"
Parameters: source files (wildcards supported), -sEML sets the target format, and the last argument is the output folder. Save this command in a .bat file and schedule it with Windows Task Scheduler to automate nightly MSG-to-EML exports. The command-line version supports all options available in the GUI: file naming patterns, folder structure, and attachment handling.
| Feature | Manual (drag from Outlook) | Total Mail Converter |
|---|---|---|
| Batch export | One email at a time | Entire folders — thousands of files in one click |
| Attachment handling | Embedded, no control | Embedded as MIME parts, full control |
| Folder structure | Lost — all files in one pile | Preserved — subdirectories mirrored |
| File naming | Outlook's default (cryptic) | Custom patterns: Date, Subject, Sender |
| Speed | Manual drag-and-drop per file | Thousands of files per minute |
| Requires Outlook | Yes | No — reads MSG files independently |
| Command-line automation | Not possible | Full CLI with all options |
| Pricing | Requires Outlook license | $59.90 one-time, 30-day free trial |

Download the free 30-day trial — no email or credit card required. A personal license costs $59.90 and includes one year of free upgrades. Works on Windows 7/8/10/11.
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"We migrated 40 staff mailboxes from Outlook to Thunderbird. Each user had years of MSG files exported from PST archives. Total Mail Converter processed all of them in batch — around 12,000 MSG files total. Every EML imported into Thunderbird cleanly: headers, body formatting, attachments, all intact. The file naming by date and subject made the transition transparent to end users."
Brian Kowalski System Administrator, Greenfield Municipal District
"We receive custodian email exports as MSG files and need to standardize them to EML for our forensic analysis platform. Total Mail Converter preserves the full MIME structure, including all original headers and routing information. The command-line mode lets us script the conversion into our evidence intake workflow. Reliable output every time."
Sandra Reeves Digital Forensics Analyst, Reeves & Associates
"Clients regularly hand me MSG files they cannot open because they switched from Outlook to Apple Mail or Thunderbird. Total Mail Converter handles the conversion quickly — even folders with 5,000+ files. The batch mode and custom naming save hours of manual work. Only wish: a native Mac version so I could run it without a VM."
Martin Delgado IT Consultant, Delgado Tech Solutions
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