How to Import Zimbra to Thunderbird (TGZ to MBOX)

Quick Answer

To import Zimbra to Thunderbird, add the live account to Thunderbird over IMAP and drag the folders into Local Folders. If the server is gone, convert the .tgz export to MBOX with the Univik Zimbra Converter and load it through the ImportExportTools NG add-on. Thunderbird keeps the folder tree, attachments and dates either way.

Mozilla Thunderbird is the usual landing spot when a team leaves Zimbra but still wants a free desktop mail app rather than a web client. The catch is that Thunderbird will not read a Zimbra .tgz on its own, and it has no import button for old mail in the plain install. So the move comes down to three routes, and the right one depends on whether the Zimbra server is still running or you are left with an export. This guide walks all three and shows what each brings across.

Why Import Zimbra Mail into Thunderbird

Most people who import Zimbra to Thunderbird are moving off a hosted or self-run Zimbra and want their old mail to sit locally, searchable and offline, without a subscription. Thunderbird stores each folder as a plain MBOX file on the disk, so once the mail is in, it is yours to back up or copy anywhere. Others keep Thunderbird as a reading archive while the live accounts move to something else. Whatever the reason, the old Zimbra folders have to arrive whole, with attachments and dates intact.

Three Ways to Import Zimbra to Thunderbird

Two of the three routes work from a Zimbra export, so no live server is needed and the full mailbox comes across. The IMAP route instead reads a running account and mirrors the folders as they stand. Pick by what you are holding rather than by which sounds quickest.

1. Add the account over IMAP

Server still up? Add Zimbra to Thunderbird as an IMAP account and drag the folders into Local Folders.

2. Convert the .tgz to MBOX

Have a .tgz and no server? Write one MBOX per mailbox, then import it with ImportExportTools NG.

3. Drag the EML files in

Only a handful of mails? Extract the archive and drag the .eml files straight into a Local Folder.

Three routes from Zimbra into Thunderbird, each suited to a different starting point

Add the Zimbra Account to Thunderbird over IMAP

When the Zimbra server is still up, this is the fastest way in and it costs nothing. Thunderbird connects to the account and shows the folders as they sit on the server. From there you copy the ones you want down to your own machine. Turn on IMAP for the account in Zimbra first, then set it up in Thunderbird with the server address and the secure IMAP port 993.

Add the account in ThunderbirdOpen Account Settings and add a mail account. Enter the Zimbra address and password, and choose IMAP when asked for the account type.
Point it at the Zimbra serverSet the incoming server to the Zimbra host on port 993 with SSL, so the folders load over a secure link.
Copy folders into Local FoldersDrag each Zimbra folder onto Local Folders in the left pane. Thunderbird downloads the mail and keeps it after the account is gone.

The IMAP route mirrors mail folders only. Contacts and the calendar are handled separately, which the last section covers. If the server has already been shut down, skip ahead to the export routes.

Convert the Zimbra TGZ to MBOX and Import It

This is the route for a dead server or a folder of .tgz files, and it is the one that scales to many mailboxes. To import a Zimbra TGZ to Thunderbird here, you run a Zimbra to MBOX conversion first, since MBOX is the format Thunderbird keeps mail in. Turn each .tgz into an MBOX file, then load that file with a small free add-on. The Univik Zimbra Converter opens the .tgz and produces clean MBOX that already holds the folder tree, the attachments and the dates. It can write EML as well when you want the messages as loose files.

Convert the .tgz to MBOXLoad the export into the Univik Zimbra Converter and choose MBOX as the output. One MBOX file comes out for each mailbox folder.
Install ImportExportTools NGIn Thunderbird open the add-ons page, search for ImportExportTools NG and add it. This is what gives Thunderbird an MBOX import.
Import the MBOX fileRight-click on Local Folders and open ImportExportTools NG, or reach it from the Tools menu. Pick Import mbox file, then Import directly one or more mbox files. Choose what the converter wrote.
Check the foldersOpen the new folder in Thunderbird and compare the message count with Zimbra so you know the whole mailbox landed.

Univik Zimbra Converter start screen with Open, Review and Export steps for turning a Zimbra mailbox into MBOX for Thunderbird — The converter opens on a plain Open, Review and Export flow

If you would rather reach Outlook from the same export, our guide on how to convert Zimbra to PST takes the .tgz the other way, and how to migrate Zimbra to Office 365 covers the cloud move. The converter writes all of these from one .tgz.

Univik Zimbra Converter export menu with MBOX as a target, alongside EML, PST and Gmail, for importing Zimbra mail into Thunderbird — The Export menu lists MBOX and EML, the two formats Thunderbird reads through ImportExportTools NG

Drag Zimbra EML Files into Thunderbird

For a small or selective move, the EML route is the simplest. Export the mailbox as EML, or extract the .tgz, so each message sits as its own .eml file inside the folder tree. Then drag those files straight into a Local Folder. With ImportExportTools NG installed you can also import a whole folder of EML in one go, which keeps the subfolders.

Get the mail as EMLExport Zimbra mail from the Zimbra Web Client under Preferences then Import/Export. Or open the .tgz and pull out the .eml files with 7-Zip or WinRAR.
Make a Local FolderRight-click Local Folders in Thunderbird and add a new folder to hold the imported mail.
Drag the EML inSelect the .eml files and drop them into the folder, or use ImportExportTools NG to import the whole EML directory at once.

Loading a Zimbra .tgz export in Univik Zimbra Converter before writing MBOX for Thunderbird — Point the tool at the exported .tgz, or sign in to read a live account

Bring Zimbra Contacts and Calendar into Thunderbird

Mail is only part of a mailbox. Zimbra contacts and the calendar move on their own tracks, and Thunderbird has a home for each. Save the address book as a vCard and import the .vcf into the Thunderbird Address Book. Save the calendar as an ICS file and open it in the built-in Thunderbird calendar, once known as Lightning. The Univik Zimbra Converter drops a .vcf and an .ics beside the mail on the EML export, so both are ready without a second tool.

Mail (MBOX or IMAP)

Folder tree, attachments, sender and sent date, read and unread marks.

Contacts (vCard)

A .vcf file loads into the Thunderbird Address Book in one import.

Calendar (ICS)

An .ics file opens in the built-in Thunderbird calendar as its own entry.

What reaches Thunderbird, and the file each part travels in

The one thing people forget is the add-on. Thunderbird looks like it should import mail on its own, so they hunt for a menu that is not there. Install ImportExportTools NG first and the MBOX route stops being a fight.

U

The Univik Team

Desktop mail conversion

Conversion software since 2013

Tested and Verified: Zimbra to Thunderbird Results

We tested this rather than take the steps on faith. The team ran real Zimbra archives through the MBOX route and loaded them into a fresh Thunderbird profile with ImportExportTools NG. Sample data covered Zimbra Collaboration builds between 8.8.15 and the 10.x releases, plus one Zimbra Desktop store. In each import the folder tree matched the source. The message count lined up and attachments opened as they had on Zimbra. Sender names and sent dates stayed in place, and a vCard of contacts plus an ICS calendar loaded cleanly into the Address Book and the calendar.

8.8.15–10.x

Zimbra builds checked, Zimbra Desktop included

Folder match

the tree rebuilt the same way in Thunderbird

Dates kept

sender and sent date stayed on each mail

vCard + ICS

contacts and calendar loaded on their own

How the Zimbra to Thunderbird MBOX route held up in Univik testing

Zimbra to Thunderbird Questions

No. A .tgz is a gzipped tar archive, and Thunderbird has no reader for it. You either extract the archive and load the messages inside, or turn the .tgz into an MBOX file, which is the format Thunderbird stores mail in. Both paths are covered below.

If the Zimbra server is still up, add the account to Thunderbird over IMAP and drag the folders you want into Local Folders. Nothing to export, nothing to convert. When the server is gone and all you hold is a .tgz, convert it to MBOX and load that with the ImportExportTools NG add-on instead.

They can, but not through the mail import. Save the contacts as a vCard and bring them into the Thunderbird Address Book. Save the calendar as an ICS file and open it in the Thunderbird calendar. The Univik Zimbra Converter writes a .vcf and an .ics next to the mail so both are ready to load.

Only the IMAP route needs it, since that one reads the account live. Both export routes work offline. As long as you hold the .tgz files, a powered-down or even a failed Zimbra box is no obstacle. Everything then happens on your own PC.

Yes. The MBOX import through ImportExportTools NG rebuilds the folder tree, so the Zimbra folder hierarchy stays intact. Every message keeps its attachments, its sender and its sent date. Read and unread marks carry too. The IMAP route mirrors the folders as they sit on the server.

It is a free Thunderbird add-on that lets Thunderbird import and export MBOX files and EML messages, which the plain program cannot do on its own. For the offline routes you install it once from the Thunderbird add-ons page, then use it to pull the MBOX or the EML folder in.

Yes, with the offline route. Load the whole set of .tgz files into the Univik Zimbra Converter, write one MBOX per account, then import each into its own Local Folder. The conversion runs as a batch, so a large set is a single unattended pass rather than one mailbox at a time.

The IMAP route is free and needs only a running server. The ImportExportTools NG add-on is free too, but you still need MBOX files to feed it. Turning a raw .tgz into clean MBOX by hand is slow. The converter is the paid shortcut for a dead server or a bulk job.

Leena Taylor Paul

Written by Leena Taylor Paul for Univik, a maker of Windows email and file utilities running since 2013. Thunderbird makes you choose between a live IMAP pull and an offline file import, so this guide sticks to matching the route to what you hold and to proving that folders, attachments and dates all arrive. Last reviewed September 2026. Stuck on which route to take? Talk to our support team.