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. DBX is Outlook Express’s old per-folder mailbox format, and Thunderbird cannot read loose .dbx files, so you convert them to MBOX or EML first. To import DBX files to Thunderbird, convert the .dbx with the free DbxConv tool, then import the resulting MBOX with ImportExportTools NG, or let a converter do the whole set in one pass.
On this page
What a .dbx file really is?
A little background makes this whole job clearer. A .dbx file belongs to Outlook Express, Microsoft’s old email client from the Windows XP era, long since discontinued. Outlook Express saved each folder as its own .dbx, so you end up with Inbox.dbx, Sent Items.dbx and so on, plus a Folders.dbx that is just the master index. Each of those is a little database of messages, in a closed format only Outlook Express truly understood. Thunderbird speaks the open formats instead, it stores mail as MBOX and reads EML, and it has no reader for .dbx. So the move is really a format change, convert the .dbx to MBOX or EML first, and then Thunderbird takes it happily.
Each Outlook Express folder is a .dbx, convert them to MBOX or EML for Thunderbird.
“DBX is one of those legacy formats where the sensible move is to get out of it entirely. Each .dbx is an Outlook Express folder in a closed layout, and the moment you convert it to MBOX or EML the data is in an open format that Thunderbird, Apple Mail and almost anything else can read. The free DbxConv tool does that conversion cleanly for a set of folders, and once you have the MBOX, Thunderbird’s own import finishes it. For a large or messy Outlook Express store a dedicated converter saves the fiddly bits and keeps attachments, but either way the goal is the same, leave DBX behind.” Shubham Dixit, Data File Conversion reviewer (draft, pending approval)
About Thunderbird’s built-in import
You may have read that you can just open Thunderbird, go to Tools, then Import, and pick Outlook Express. That is only half true, and it trips a lot of people up. That built-in importer works only when you are on the same old Windows PC that still has Outlook Express installed, because it reads the live Outlook Express profile, not loose .dbx files sitting in a folder. If you are on a newer Windows, a Mac, or you simply have a pile of .dbx files copied from an old drive, that option will not find them. In that far more common situation, you convert the .dbx first, which is exactly what the next section does.
The free way, convert then import
There is a free, well-loved tool for this. DbxConv is a small, portable, open-source converter that turns Outlook Express .dbx files into standard formats, no install needed. Drop your .dbx files next to it and run DbxConv *.dbx to produce MBOX files, or DbxConv -eml *.dbx to get individual .eml files instead. Skip Folders.dbx, since that is only the index, not a mail folder. A free alternative, undbx, does much the same, extracting each .dbx into .eml messages.
Now bring the result into Thunderbird. Install the free ImportExportTools NG add-on, right-click Local Folders, choose ImportExportTools NG, then Import mbox file and pick the MBOX you made, or, if you exported .eml, choose Import all messages from a directory and point it at the folder. Your old Outlook Express mail lands in Thunderbird, folders and attachments intact, and none of it cost anything.
Convert the .dbx for free with DbxConv, then import the MBOX into Thunderbird.
The bulk way, a converter
If you have a whole Outlook Express store, or you would rather skip the command line, a converter reads the .dbx files and hands them to Thunderbird in one go. The PCDOTS DBX Converter loads your .dbx files, previews the messages, and exports to MBOX for Thunderbird, or straight to a Thunderbird profile, keeping attachments and folder structure. It works without Outlook Express installed, which matters because OE will not run on a current Windows, so orphaned .dbx files convert fine. It runs on Windows with a free trial for the first ten items so you can confirm it reads your files first. For a big or awkward store, this is the low-effort path.
The tool route, a set of .dbx files exported straight to MBOX or 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 DBX files and add your Outlook Express files.
Step 3. Open Export and choose MBOX, or Thunderbird directly.
Step 4. Pick a destination and save.
Related reading, our guides to import Windows Live Mail to Thunderbird and import an MBOX into Thunderbird. To check the converted mail first, the free MBOX viewer opens the .mbox without any client.
Opening .dbx on a Mac
A common question, since Outlook Express never really lived on the Mac. A .dbx is a Windows format, so macOS has nothing that opens it directly. The route is the same idea, convert first. Run the .dbx through DbxConv to make MBOX or EML, then open that in Apple Mail or Thunderbird on your Mac, both of which read those formats natively. If the .dbx files are on an old Windows PC, doing the conversion there and copying over the MBOX is often the tidiest way.
The methods compared
All roads end with your Outlook Express mail in Thunderbird, so choose by your setup.
| Method | Best for | Good to know |
|---|---|---|
| Built-in OE import | Old PC with OE installed | Will not read loose .dbx |
| DbxConv plus import | Loose .dbx, free | Command line, then import |
| DBX Converter tool | A whole store, no OE | Windows, one pass, preview |
Frequently asked questions
Can Thunderbird open a .dbx file directly?
No. Thunderbird reads MBOX and EML, not Outlook Express DBX. Convert the .dbx to MBOX or EML first, then import it.
How do I import DBX files to Thunderbird for free?
Convert the .dbx with the free DbxConv tool to MBOX or EML, then import the result using Thunderbird’s ImportExportTools NG add-on.
Why does the built-in Outlook Express import not work for me?
It only reads a live Outlook Express profile on the same old Windows PC. For loose .dbx files or a newer machine, convert the files instead.
Do I need Outlook Express installed?
No. DbxConv and a dedicated converter both read .dbx without Outlook Express, which is essential since OE will not run on current Windows.
Should I skip Folders.dbx?
Yes. Folders.dbx is just the master index, not a mail folder, so leave it out of the conversion and convert the named folder files.
Can I do this on a Mac?
Not directly, since DBX is a Windows format. Convert the .dbx to MBOX or EML first, then open that in Apple Mail or Thunderbird on the Mac.
Out of a dead format at last
It is worth stepping back to see what you have gained here. Outlook Express and its .dbx files have been out of support for years, and mail trapped in that format only gets harder to reach as machines age. The moment you convert those .dbx files to MBOX or EML, your email is in an open, portable format that Thunderbird reads today and that Apple Mail or almost any future client will read tomorrow. So convert with the free DbxConv, or a tool for a bigger store, import into Thunderbird, and your old messages are finally free to travel wherever you go next.
