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. Maildir stores each email as a separate file, while Thunderbird keeps folders as MBOX, so you import rather than copy. The free way is the ImportExportTools NG add-on, which pulls all the message files from a Maildir folder into Thunderbird. For a whole server tree you can convert the Maildir to MBOX first, or use a tool.
On this page
What Maildir is, and why you import it?
Maildir is not an email program, it is a way of storing mail. Each message sits in its own file inside a folder, and every Maildir folder has three subfolders, cur for messages already stored, new for freshly delivered ones, and tmp for deliveries in progress. It is the format many Linux mail servers use, Dovecot, Courier, qmail and Postfix among them, so you usually meet a Maildir after copying a mailbox off a server.
Thunderbird, by contrast, stores each folder as a single MBOX file. Because the two keep mail in different shapes, you cannot just drop a Maildir into Thunderbird’s folder, you import the messages so Thunderbird can file them its own way. Here is the free route, then the options for a bigger job.
Two different shapes, so you import the messages rather than copy the folder.
“The thing to hold onto is that Maildir is a storage format, not an application, so importing it means feeding those individual message files into Thunderbird. The ImportExportTools NG add-on does exactly that, it reads every file in a directory and files them as real messages. I only reach for a converter when someone hands me a whole server tree with dozens of folders to keep in order, or they also want the mail as PST or in another account. For one mailbox, the free add-on is enough.” Shubham Dixit, Email Migration reviewer (draft, pending approval)
Does Thunderbird support Maildi?
Partly, and it helps to be precise about it. Thunderbird has an experimental Maildir storage option you can switch on in the Config Editor before creating an account, which makes Thunderbird store its own mail as Maildir instead of MBOX. That is about how Thunderbird keeps new mail, though, not a button that imports an existing server Maildir. For bringing in a Maildir you already have, the add-on below is the practical route, and it works whatever storage mode you use.
Free, the ImportExportTools NG add-on
This is the free way, and the same add-on is the usual answer for importing almost anything into Thunderbird. ImportExportTools NG can read a directory full of message files, which is exactly what a Maildir is.
Open the Add-ons manager in Thunderbird, search for ImportExportTools NG, and add it. Make a local folder to hold the mail, then right-click it, choose ImportExportTools NG, then Import messages, and pick all messages from a directory, with the subdirectories option if the Maildir has several folders. Point it at the Maildir folder, the one holding cur and new, and it reads each file in and files it as a normal message. The Maildir files often have no extension, which is fine, the add-on treats them as messages either way.
Point the add-on at the Maildir directory, and the message files land in a Thunderbird folder.
A whole server tree, via MBOX
If you have exported a whole account with many nested folders, importing each one by hand gets slow. Since Thunderbird reads MBOX cleanly, another free path is to convert the Maildir to MBOX first, one MBOX per folder, then bring those in. A converted MBOX drops into Thunderbird by drag, or through the same ImportExportTools NG using its Import mbox option. Our guide to import MBOX into Thunderbird covers that side. This keeps the folder names and structure lined up across the whole tree.
When a tool helps
For a single mailbox the free add-on is the whole job. A tool earns its place when you have a large server export with many folders to keep in order, or you also want the mail in another format or account such as PST, EML or a live mailbox, not only in Thunderbird. The PCDOTS Maildir Converter reads a Maildir tree and exports it to Thunderbird, and to MBOX, EML, PST and services like Microsoft 365 or Gmail, on Windows, with a free version so you can preview the mail and test the layout before you buy.
The tool route, a Maildir tree straight into Thunderbird or other formats.
Here are the steps with the screens.
Step 1. Install and run the software on Windows, then open the menu.
Step 2. Choose Maildir files and add the folder so the mail loads.
Step 3. Open the Export menu and choose Thunderbird.
Step 4. Browse to a location and Save.
For the wider Thunderbird picture, see our guides to export MBOX from Thunderbird and save Thunderbird emails as EML.
After the import, where this leaves you
Once the Maildir mail is in, it stops being a pile of loose files and becomes ordinary Thunderbird folders you can search, sort and read like any other account. From there the rest is easy. You can drag those folders anywhere in Thunderbird, export any of them back out as MBOX or EML if you need to hand them on, or leave them exactly where they are. The hard part was only the format gap, and that closes the moment the messages are imported.
