# ImportExportTools NG not working? The simple fix ## What is ImportExportTools NG? ImportExportTools NG is a popular add-on (an extension) for the email program Thunderbird. People use it to export and import emails, for example to or from an mbox file. An mbox file is like a box that stores many emails one after another inside a single file. Many people rely on the add-on to make a backup, move emails to another program, or read an old archive back in. Very handy, until one day it stops working. The import button does nothing, the add-on appears greyed out, or Thunderbird freezes on a large file. In this article we calmly explain why that happens and how to fix it. And if all you really want is to peek inside your mbox without any hassle, we will show you a faster route. ## Why does ImportExportTools NG sometimes fail? Three causes are by far the most common. Almost every problem falls into one of these buckets. - **Version incompatibility.** Thunderbird updates regularly and changes under the hood. An older version of the add-on then no longer fits the newer Thunderbird, or the other way around. The result: the add-on is disabled, missing from the menu, or throws an error. - **Profile folder issue.** Thunderbird stores all your emails and settings in a so-called profile folder on your computer. If that folder sits on an external drive, in a cloud-synced folder (such as OneDrive or Dropbox), or your account lacks write permission, the add-on cannot read or write properly. The import then looks like it failed. - **File too large.** An mbox of several gigabytes (for example a multi-year archive) can slow Thunderbird down or freeze it during import. The program tries to process too much at once. In the steps below we tackle these three causes one by one. :::info title="First check: is it the add-on or Thunderbird itself?" Restart Thunderbird and see whether the problem only affects ImportExportTools NG, or whether Thunderbird in general is slow or unstable. If Thunderbird itself runs fine but only the add-on misbehaves, the cause is almost always one of the three above. ::: ## Fix 1: line up the versions Most glitches disappear once Thunderbird and the add-on are both up to date and match each other. :::howto title="Update Thunderbird and the add-on" 1. Open Thunderbird and click the menu at the top right (the three lines), choose Help, then About Thunderbird. Thunderbird now checks for updates and installs them. 2. Restart Thunderbird if an update was downloaded. 3. Open the top-right menu and choose Add-ons and Themes. 4. Find ImportExportTools NG in the list, click the gear icon next to it, and choose Check for Updates. 5. If a new version is available, install it and restart Thunderbird once more. 6. Try your import or export again. ::: :::tip title="Reinstall the add-on from scratch" If it still does not work, remove the add-on completely through Add-ons and Themes, restart Thunderbird, and install ImportExportTools NG again from Thunderbird's official add-on page. A fresh install clears up many odd hiccups. ::: ## Fix 2: check the profile folder If your Thunderbird profile sits in an awkward spot, the add-on cannot reliably read or write files. :::howto title="Check the profile folder and import safely" 1. In Thunderbird, open the top-right menu, choose Help, then Troubleshooting Information. 2. Find the Profile Folder line and click Open Folder. You now see where your profile lives. 3. If the profile is in a cloud folder (OneDrive, Dropbox, iCloud) or on an external drive, move it to an ordinary local folder on your computer, or pause cloud sync during the import. 4. Create a Local Folder in Thunderbird if you do not have one yet (right-click in the folder list, New Folder). 5. Import your mbox into that Local Folder instead of into an online account, which avoids permission and sync problems. 6. Try the import again and check that the messages appear. ::: :::warn title="Always make a copy first" Before you move your profile folder around or run large imports, make a copy of your mbox file somewhere safe. That way you can never accidentally lose your only copy if something goes wrong. ::: ## Fix 3: break up a file that is too large A very large mbox file can freeze Thunderbird. The trick is to handle it in smaller pieces. :::howto title="Make a large mbox file manageable" 1. Close other heavy programs so your computer can give all its memory to Thunderbird. 2. Do not import every folder at once, instead use ImportExportTools NG to import a single mbox file at a time. 3. Give Thunderbird time, a large file can take minutes. Wait until the progress stops before you click anything. 4. If it still freezes, split the mbox file into smaller parts before importing, and read them in one by one. ::: :::tip title="Not in the mood to split it? Just view the file directly" If you only want to read, search, or pull a few emails out of the mbox file, you do not need to import it into Thunderbird at all. With Mbox Viewer by Cloud Captains you open the file directly, whatever its size, with no add-on and no import. ::: ## The alternative: view your mbox directly, no add-on Sometimes you do not want to import at all. You just want to quickly look inside an mbox file, find something, or keep a few messages. That is exactly what Mbox Viewer by Cloud Captains is for, a free Chrome extension (see the homepage at https://mbox-viewer.online). Drag your file onto the window and you are in right away, no Thunderbird, no add-on, no import fuss. The layout feels familiar: a list of messages on the left and the open message on the right, just like Gmail or Thunderbird. It opens not only .mbox and .mbx, but also .eml, .emlx, .msg (Outlook), Maildir folders, and even .mbox.gz from Google Takeout, which it unpacks automatically. :::info title="100 percent local, your emails stay yours" Mbox Viewer runs entirely on your own device. Nothing goes to a server, there are no uploads and no tracking. Your emails are stored locally in your browser (in a database called IndexedDB) and you can wipe everything at any moment through Settings, Clear Database. External images in emails are blocked by default, so hidden tracking pixels cannot follow you. Want to see a picture anyway, you load it per message with a button. ::: The powerful search is handy too. You can search with operators like `from:`, `to:`, `subject:`, `has:attachment`, `before:2025-01-01` and `larger:5M`, put an exact phrase in quotation marks, or use `NOT` to exclude something. Organize messages with labels, stars, and your own notes. And when you want to keep or hand over emails, export them one at a time or in bulk as PDF, .eml, .html, or back to .mbox. :::tip title="Investigating or unsure about a suspicious email?" Besides Preview and Raw, every message also has a Forensic tab. There you see in plain language whether the sender is genuine (the SPF, DKIM, and DMARC result), the route the email travelled, and a suspicion score from 0 to 100 that flags phishing signals such as a fake sender name or a suspicious domain. ::: ## Summary When ImportExportTools NG fails, the cause is almost always one of three things: the add-on does not match your Thunderbird version, your profile folder is in a tricky spot, or your mbox is too large. Update everything first, import into a Local Folder, and split large files. And if you really only want a quick look inside your mbox without all that work, just open the file directly and locally with Mbox Viewer by Cloud Captains. :::faq ### Why is my ImportExportTools NG add-on greyed out or disabled? This is almost always a version incompatibility. After a Thunderbird update the old add-on no longer fits, or the add-on itself needs an update. Update Thunderbird first, then the add-on, and restart the program. If that still fails, remove the add-on and reinstall it from the official Thunderbird add-on page. ### The import seems to succeed but I see no emails, how come? Often you are importing into an online account where the folder does not become visible, or your profile folder sits in a cloud folder without the right permissions. Create a Local Folder in Thunderbird and import your mbox into it. Also check, through Help and Troubleshooting Information, where your profile lives and move it to an ordinary local folder if needed. ### Thunderbird freezes on a large mbox file, now what? An archive of several gigabytes is sometimes too much to process at once. Import a single mbox file at a time, close other programs, and give Thunderbird time. If that does not help, split the file into smaller parts. If you only want to view the file rather than import it, you can open it without any size limit directly in Mbox Viewer by Cloud Captains. ### Can I view my mbox without ImportExportTools NG or Thunderbird? Yes. With the free Chrome extension Mbox Viewer by Cloud Captains you drag the mbox file onto the window and read, search, and export your emails directly, with no add-on and no import. Visit https://mbox-viewer.online for more information. ### Is it safe to open my emails in Mbox Viewer? Yes. Mbox Viewer runs entirely locally on your own device. No emails are uploaded, there are no servers and no tracking. Everything stays inside your own browser and you can wipe it at any time. On top of that, external images are blocked by default, so tracking pixels cannot follow you. :::