Written by Jennifer Walsh. Reviewed for technical accuracy by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion.
Shubham is an independent external reviewer and not an employee of PCDOTS.
Quick answer. MSG is Outlook’s proprietary single-message format, and Thunderbird reads EML, not MSG, so there is no way to open a .msg in Thunderbird directly. To import MSG to Thunderbird, convert the .msg files to .eml first with a free tool like msgconvert, then import that folder with ImportExportTools NG, or let a converter do it in bulk.
On this page
Why Thunderbird will not open a .msg?
It helps to know why this needs a step at all. A .msg is Microsoft Outlook’s own single-message format, one email saved as a small binary file that only Outlook really understands. Thunderbird speaks a different language, it stores mail as MBOX and reads EML, the plain-text one-message-per-file format, natively. It has no built-in reader for .msg at all. So you cannot drag a .msg into Thunderbird and have it open, and there is no import button for it either. The fix is simple once you see it, convert the .msg to .eml first, and then Thunderbird reads it like any other message.
Thunderbird cannot open a .msg, but it reads .eml, so convert first.
“A .msg is an Outlook container, a compound binary file, while an .eml is plain MIME text, which is what Thunderbird expects. So the task is really a format translation, and once you have .eml files Thunderbird imports them without any fuss. For a handful of messages a free converter like msgconvert or the msg_parser library does the translation fine, just expect the odd very complex or heavily formatted message to need a second look. When there are hundreds of .msg files, especially orphaned ones with no Outlook around, a dedicated converter is the calmer path, it does the whole batch and keeps the attachments.” Shubham Dixit, Data File Conversion reviewer (draft, pending approval)
The free way, convert then import
Because Thunderbird happily reads .eml, the free path is two moves, turn your .msg files into .eml, then import them. For the conversion, a couple of free open-source tools do the job. msgconvert, from the free libemail-outlook-message-perl package, batch-converts a whole folder, you point it at your files with msgconvert *.msg and it writes an .eml beside each one. It installs through apt or Homebrew on Linux and Mac, and runs on Windows through WSL. If you prefer Python, the free msg_parser library does the same, install it with pip install msg_parser then run msg_parser -i mail.msg -e mail.eml.
Once you have a folder of .eml files, bring them into Thunderbird the easy way. Install ImportExportTools NG, right-click Local Folders, choose ImportExportTools NG, then Import all messages from a directory, and point it at your .eml folder. Every message lands in Thunderbird. It is all free, though it is worth knowing that a very complex or heavily formatted message can occasionally need a second look after conversion.
Convert the .msg to .eml for free, then import the folder into Thunderbird.
The bulk way, a converter
When there are hundreds of .msg files, or you would rather not touch a command line, a converter turns the whole batch and drops it straight into Thunderbird. The PCDOTS MSG Converter reads .msg files singly or by the folder, exports to Thunderbird directly, or to .eml or MBOX if you prefer, and keeps attachments and formatting intact. A genuine plus here, it works without Outlook, so orphaned .msg files with no Outlook on the machine convert fine. It runs on Windows with a free trial for the first ten items, so you can confirm it reads your files before buying. For a big pile of loose messages this is the low-effort route.
The tool route, a folder of .msg exported straight into Thunderbird.
Here are the tool steps with the screens.
Step 1. Install and run the software on Windows, then open the menu.
Step 2. Choose Email Data Files, then MSG, and add your .msg files or folder.
Step 3. Open Export and choose Thunderbird.
Step 4. Pick a destination and save.
Related reading, our guides to import MSG files to Apple Mail and import OLM files to Thunderbird. To check a converted message, the free EML viewer opens .eml files without any client.
Just want to open one .msg?
If your goal is only to read a single .msg and you are not moving a mailbox, the same rule applies, Thunderbird still cannot open it as is. The quickest path for one file is to convert just that .msg to .eml with msgconvert or msg_parser, then double-click the .eml or drag it into a Thunderbird folder. If you would rather not install anything and you still have Outlook, opening the .msg in Outlook is of course the simplest read of all. But to get it into Thunderbird specifically, the .eml conversion is the step you cannot skip.
The methods compared
Both end with your mail in Thunderbird, so pick by how many files you have.
| Method | Best for | Good to know |
|---|---|---|
| msgconvert or msg_parser | A few files, free | Command line, then import |
| MSG Converter tool | Hundreds of files | Windows, no Outlook, one pass |
| Open in Outlook | Just reading one | Not a move to Thunderbird |
Frequently asked questions
Can Thunderbird open .msg files directly?
No. Thunderbird reads EML and MBOX, not Outlook’s MSG format. Convert the .msg to .eml first, then Thunderbird opens it.
How do I import MSG to Thunderbird for free?
Convert the .msg files to .eml with a free tool like msgconvert or msg_parser, then import that folder using Thunderbird’s ImportExportTools NG add-on.
Do I need Outlook installed to do this?
No. The free converters and a dedicated tool both read .msg without Outlook, which is handy for orphaned .msg files on a machine with no Outlook.
Will attachments come across?
Yes. A proper .msg to .eml conversion keeps attachments and formatting, though a very complex message is worth a quick check afterward.
What is the fastest way for hundreds of .msg files?
A converter that reads a whole folder and exports to Thunderbird in one pass, so you skip converting and importing each file yourself.
Why is there no direct MSG import in Thunderbird?
Because MSG is Outlook’s proprietary binary format and Thunderbird was built around the open EML and MBOX formats, so it never included an MSG reader.
The one thing to remember
If you take only a single idea from this, make it this one, Thunderbird cannot read a .msg, so everything comes down to turning those files into .eml first. Do that with a free converter for a few messages, or a bulk tool for a mountain of them, and the import into Thunderbird is the easy part either way. Get to .eml, and you are essentially done.
