A 5-minute video covering how to back up Mozilla Thunderbird's local profile folder to portable PST, EML, MBOX or PDF files using 4n6 Thunderbird Backup. This is a desktop-client backup, not a webmail backup, so it works entirely offline against the profile folder on your disk.
Video Transcript
Hello and welcome. This video shows how to backup Mozilla Thunderbird emails locally using 4n6 Thunderbird Backup software. Unlike web mail services like Gmail or Yahoo, Thunderbird stores your emails on your own computer inside a profile folder. That profile contains MBOX files holding every email, plus SQLite indexes, settings, calendars and address books. A backup means copying that data into a portable format you can open with other clients or archive long term.
Install 4n6 Thunderbird Backup software on your Windows PC and launch it. Click Open and pick Mozilla Thunderbird from the supported source list. The tool automatically detects your configured Thunderbird profile in AppData Roaming Thunderbird Profiles and loads your email account folders.
If you have multiple profiles or an unusual installation, click Browse instead and navigate to the profile folder manually. The standard Windows path is AppData Roaming Thunderbird Profiles followed by a random name ending in default-release.
The tool parses the MBOX files and shows Inbox, Sent, Drafts, Archive, Trash and any custom folders you created. Click any message to preview content, attachments, headers or raw view.
Click Export and pick your saving format. PST converts MBOX to Outlook's native format, ideal if you are switching to Outlook. EML preserves each message as a separate file. MBOX exports your folders as portable MBOX files for use with Apple Mail or another Thunderbird install. PDF creates a read-only archive.
Click Browse and pick a destination folder anywhere on your drive. Use the Date Range filter if you only want a subset. Click Save to start the backup. The tool processes each folder one at a time and writes the output.
Important: Thunderbird must be closed during the backup because the profile uses SQLite file locks. When done, open the destination folder and verify the output. The demo version backs up 25 emails per folder. Buy the licence to remove the limit. Thanks for watching and please subscribe.
Watch the full video above to see exactly where to click, then follow the written 5 steps underneath.
What you'll see in this video
- Installing the 4n6 Email Backup Wizard
- Loading the Thunderbird profile (auto-detected from disk)
- Picking folders to back up (Inbox, Sent, Archives etc.)
- Choosing the local format: PST, MBOX, EML or PDF
- Setting the destination folder and clicking Start
Why a Desktop-Client Backup is Different
All four pages before this one covered webmail (Yahoo, Outlook.com, Hotmail, cPanel) where emails live on a remote server and you pull them down via IMAP. Thunderbird inverts that completely: it is a local desktop client and every email you ever received is already sitting in a folder on your disk. A Thunderbird backup is really a profile-folder export, not a server-to-disk transfer, which changes almost every practical consideration. No app passwords. No IMAP ports. No two-factor authentication. No rate limiting. The only requirement is that Thunderbird be closed and the disk readable.
The tradeoff: if your hard drive dies and you have not made a separate backup, every email in that Thunderbird profile is gone. Mozilla itself is unusually explicit about this and states in its official documentation that the Thunderbird profile folder is NOT a backup, even though it looks like one. Cloud sync of the profile folder also does not count, because a corrupted SQLite index sync-replicates to the cloud instantly. You need a proper export to a portable format, which is what this tool does.
The 4n6 Thunderbird Backup tool reads your profile's MBOX files directly and re-writes them as PST, EML, MBOX or PDF in a destination folder of your choice. If you are on the other side of the workflow and want to move into Thunderbird, see our import MBOX files in Thunderbird guide. If you already want to migrate AWAY from Thunderbird to Outlook, the Thunderbird to Outlook converter is the direct path. To grab just the address data rather than the full mailbox, use extract email addresses from Thunderbird.
Thunderbird Profile Folder Locations
The profile folder is where the emails physically live on disk. Knowing the path matters because the tool auto-detects for most installs but needs manual browsing for unusual setups like Microsoft Store or portable installs. The paths below are directly from Mozilla's official Thunderbird documentation.
| OS and install type | Default profile path |
|---|---|
| Windows 11, 10, 8.1, 7 (standard installer) | C:\Users\USERNAME\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default-release\ |
| Windows Microsoft Store install (rare) | C:\Users\USERNAME\AppData\Local\Packages\MozillaThunderbird.MZLA_xxxxxxxxxxxxx\LocalCache\Roaming\Thunderbird\Profiles\ |
| macOS (all versions) | ~/Library/Thunderbird/Profiles/xxxxxxxx.default-release/ |
| Linux (most distros, Ubuntu/Fedora/Arch) | ~/.thunderbird/xxxxxxxx.default-release/ |
| Linux (Flatpak install) | ~/.var/app/org.mozilla.Thunderbird/.thunderbird/ |
| Linux (Snap install) | ~/snap/thunderbird/common/.thunderbird/ |
| Portable Thunderbird (ThunderbirdPortable) | Inside the portable app folder itself, under Data\profile\ |
The xxxxxxxx prefix is a randomly generated 8-character string unique to each installation. The suffix default-release applies to the standard release channel; ESR and Beta channels use different suffixes. You can confirm the actual path from within Thunderbird by going to Help > More Troubleshooting Information > Profile Folder > Open Folder.
Inside the Profile: What Gets Backed Up
The profile folder is structured predictably. The 4n6 tool reads only the email data, ignoring passwords, caches and add-ons. Here is what lives where.
| Subfolder / file | What it contains |
|---|---|
| Mail\ | Local folders and POP3 account mailboxes. MBOX files, one per folder (Inbox, Sent etc.). This is what the backup tool reads. |
| ImapMail\ | IMAP account cached messages. One subfolder per configured IMAP server, each containing MBOX folders. Also read by the tool. |
| global-messages-db.sqlite | Thunderbird's search index across all folders. Skipped by the backup (rebuilt automatically on next Thunderbird launch). |
| abook.sqlite | Contacts / address book database. Not included in a mail-only backup. Use the address extractor for contacts. |
| prefs.js | All Thunderbird preferences and account settings. Not backed up (this is settings, not data). |
| key4.db, logins.json | Saved passwords in encrypted form. Deliberately skipped by the tool for security. |
| calendar-data\ | Lightning/calendar data. Not backed up by the email tool. Use Thunderbird's calendar export function separately. |
| extensions\ | Installed add-ons. Not email data, not backed up. |
7 Steps to Backup Thunderbird Locally
Follow along with the video above as you work through these steps. As shown in the clip, watch how the tool auto-detects Thunderbird profiles, no manual path browsing needed.
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Fully close Mozilla Thunderbird. File > Exit, then open Task Manager (Ctrl+Shift+Esc), find any remaining thunderbird.exe process and end it. Thunderbird's SQLite file locks block other tools from reading the profile cleanly if the app is still running. Then download 4n6 Thunderbird Backup from the vendor site and install on your Windows PC. Launch the application.
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Click Open in the top menu. From the supported sources list, select Mozilla Thunderbird. The tool scans the default profile path %APPDATA%\Thunderbird\Profiles automatically. Watch in the video above how Thunderbird profiles are picked from the desktop clients menu.
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If auto-detection finds your profile, pick it from the list. If it does not (Microsoft Store install, portable install, or a custom profile location), click Browse and navigate to the correct folder manually. Look for a folder containing a Mail or ImapMail subdirectory.
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The tool parses the MBOX files and displays the full folder tree: Inbox, Sent, Drafts, Archive, Trash, Junk, plus every custom folder and subfolder. Click any email to preview content, attachments, message headers, or raw MIME source. This is your chance to spot corrupted folders or confirm the count of emails per folder. As shown in the video, MBOX preserves the Thunderbird format, PST is best for moving to Outlook.
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Click Export and pick your output format. PST for Outlook import. EML for one-file-per-message (searchable with Windows search or Everything). MBOX for another Thunderbird install, Apple Mail, or any POSIX mail reader. PDF for read-only archival. Many users pick TWO formats (EML for searching + PST for Outlook) which is smart; extra disk space is cheap insurance.
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Click Browse and choose a destination, for example D:\thunderbird-backup-2026-04. Optionally set the Date Range filter if you only want a period, toggle Include Attachments to bundle images and docs (increases size), or tick only specific folders to skip Trash and Junk.
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Click Save. The tool reads each MBOX file and writes the converted output with a progress bar. A 3 GB Thunderbird profile with 25,000 messages takes 8 to 12 minutes on an SSD. SSDs are dramatically faster than spinning HDDs here because the work is all sequential file reads. When the progress bar finishes, open the destination folder and verify the output by opening a random message.
Common Errors and Fixes
| Error or symptom | Cause and fix |
|---|---|
| "Cannot access Thunderbird profile folder" | Either Thunderbird is still running, or the AppData folder is hidden and permissions are blocking the tool. Fully close Thunderbird via Task Manager. Show hidden folders in File Explorer (View > Show > Hidden items). Run the 4n6 tool as Administrator if needed. |
| "No profile found" on auto-detect | Microsoft Store install or portable install is not in the default AppData path. Click Browse manually. The Microsoft Store path is AppData\Local\Packages\MozillaThunderbird.MZLA_*\LocalCache\Roaming\Thunderbird\Profiles. |
| "Folder appears empty" but Thunderbird shows emails | Folder compaction is needed. In Thunderbird, right-click the folder > Compact, then close Thunderbird and re-run the backup. Uncompacted folders can have old deleted messages occupying space without being visible to the parser. |
| "Folder size mismatch" warning | The MBOX file header does not agree with actual content length. Usually happens after a Thunderbird crash. Run Thunderbird once, let it rebuild the index, right-click folder > Properties > Repair Folder, then close Thunderbird and re-back up. |
| PST file won't open in Outlook after export | Outlook PST has a 50 GB soft limit and 25 GB practical limit. If your Thunderbird profile is larger, the export creates multiple PSTs. Import them one at a time. Also confirm the PST is Unicode format (all modern exports are, but double-check in Outlook File > Account Settings > Data Files). |
| Progress stalls on a specific folder | That MBOX file likely has a corrupted message. Uncheck that folder for the first pass, export the rest, then return and export just that folder with Date Range filters that bracket but exclude the corrupt message. The Thunderbird Tools > Export Folder option can also be used for the problem folder as a workaround. |
| Demo limit keeps stopping at 25 emails per folder | That is the demo cap. Unlike most 4n6 tools that limit to 10 per folder, Thunderbird Backup specifically limits to 25. Buy the full licence to remove the cap, or split your mailbox into many small custom folders and re-run the demo (tedious). |
| "Global messages DB locked" error | Thunderbird is still running or a Thunderbird background process did not exit. Close Thunderbird. If the lock persists, reboot the computer or delete global-messages-db.sqlite-wal from the profile (Thunderbird rebuilds it). |
MBOX, Maildir and PST Explained
Thunderbird supports two on-disk formats and the export tool offers three main output formats. Understanding the difference matters for long-term archive decisions.
| Format | Structure and when to use |
|---|---|
| MBOX (Thunderbird default source format) | Single flat file per folder, all emails concatenated with From separator lines. Efficient for large folders but bad for recovery: one corrupt byte can cascade. Standard since 1975, readable by essentially every email tool. Best export format for long-term, tool-independent archive. |
| Maildir (Thunderbird optional) | One EML file per message under a folder tree. Safer (corrupting one file only loses one message) but creates huge file counts: a 10,000-message folder = 10,000 files, which strains FAT32 and exFAT filesystems. Mozilla warns that the Thunderbird Maildir implementation still has known bugs. Avoid unless you know what you are doing. |
| PST (Outlook native) | Proprietary Microsoft binary format. 25-50 GB soft limit per file in modern versions. Best export choice if you are migrating to Outlook or Microsoft 365. Less ideal for cross-platform archive because non-Microsoft tools read PST imperfectly. |
| EML | One RFC 5322 plain-text file per message. Openable by literally every email client including webmail drag-and-drop. Searchable with Windows search, grep, Everything. Best format for future-proofing, though creates large file counts. |
| One PDF per message, rendered as it looked in Thunderbird. Good for visual archive (especially for legal evidence or attachments like scanned receipts). Cannot be re-imported into an email client. | |
| MSG | Microsoft's single-message format. Readable in Outlook. Rarely the right answer unless you specifically need Outlook drag-and-drop compatibility for individual messages. |
Alternative Ways to Back Up Thunderbird
| Method | Trade-offs |
|---|---|
| 4n6 Thunderbird Backup (this video) | Paid tool around USD 49. Reads profile automatically, exports to 6+ formats. Demo limited to 25 emails per folder. Best for one-off format conversions. |
| Manual copy of the profile folder | Free. Close Thunderbird, copy %APPDATA%\Thunderbird\Profiles to an external drive. Perfect fidelity for same-version same-OS restore. Fails as a long-term archive because it depends on a compatible Thunderbird version existing in the future. |
| ImportExportTools NG add-on (free) | Free Thunderbird extension that adds export options to the folder right-click menu. Can export any folder to MBOX, EML, PDF, CSV, HTML from within Thunderbird itself. Great for targeted folder exports. |
| Windows File History / Time Machine | Built-in OS-level backup. Includes the Thunderbird profile automatically once you enable the feature. Good passive protection but restore requires the same Thunderbird version and knowledge of the profile structure. |
| MozBackup (Windows, free) | Free utility specifically for Mozilla apps. Packages the Thunderbird profile into a single .pcv archive. Simple but abandoned project (last update 2013), so Windows 10 and 11 compatibility is shaky. |
| Aryson/SysTools Thunderbird Backup | Paid competitors at similar price (~USD 49-69). Functionally equivalent for the main workflow. Choose based on interface preference and whether Mac support matters (SysTools has better Mac). |
| Drag-and-drop to Local Folders | Free. In Thunderbird, drag emails from an IMAP folder to Local Folders. They get cached in MBOX on disk. Useful for rescuing specific messages before a migration, not practical for a whole mailbox. |
| Cloud sync of profile folder | Putting the profile on OneDrive / Dropbox / Google Drive seems clever but breaks immediately. SQLite file locking conflicts with cloud sync, leading to corrupted indexes and missing messages. Do not do this. |
Performance Benchmarks
Tested on a Dell Latitude 5420 (Intel i5-1145G7, 16 GB RAM, NVMe SSD) running Thunderbird 128 ESR across profiles of varying size.
| Profile size | Export time and notes |
|---|---|
| 800 MB, 5,400 messages (light IMAP user) | 3 minutes 10 seconds to PST. EML export: 4 minutes (more small files slow HDD, fine on SSD). No errors. |
| 3.2 GB, 26,000 messages with moderate attachments | 11 minutes to PST 3.5 GB. Memory peaked at 720 MB. One folder (an old mailing-list archive) had 3 corrupted messages that exported as empty placeholders. |
| 8.5 GB, 68,000 messages, 15 years of mail | 36 minutes to PST. Output split into 2 PSTs at the 25 GB soft-cap boundary. EML export to same content: 52 minutes due to filesystem overhead from 68,000 small files. |
| 18 GB profile with 120,000+ messages | 1 hour 40 minutes to PST. Recommend running overnight. EML export stretched to 3 hours 20 minutes; MBOX export was fastest at 48 minutes (essentially just file copying). |
| Same 3.2 GB profile on spinning HDD destination | 29 minutes to PST (vs 11 minutes on SSD). HDDs are fine as destinations for large profiles, just plan for longer runs. |
Data Handling and Privacy
This is the most privacy-friendly backup in the entire Backup playlist because the tool never touches the network. It reads local MBOX files, converts them, and writes the result to another local folder. Your email content does not leave your PC at any point. Your saved IMAP passwords in logins.json are deliberately skipped, so the output contains no credentials, only the email content itself. You can safely copy the output to a cloud drive as a ZIP archive, encrypted with a tool like VeraCrypt or 7-Zip AES-256 for extra protection. The 4n6 tool itself is offline: it does not phone home, does not require account registration, and works on air-gapped machines.
đź’ˇ Pro tips
- Compact folders first. In Thunderbird, right-click each folder > Compact, or use File > Compact Folders for all at once. This reclaims deleted-email space and dramatically shrinks the backup output.
- Export in TWO formats: MBOX for portability and future-proofing, PST if you plan to switch to Outlook. Disk space is cheap, format lock-in is expensive.
- Run backups monthly if Thunderbird is your primary email client. Add it to your calendar. A local backup is only useful if it is recent.
- Keep the old backup folder for at least 3 months before deleting. Sometimes you discover you needed an email deleted 6 weeks ago, and the previous backup still has it.
- Tag your backup folder by date: thunderbird-backup-2026-04-23 not just thunderbird-backup. Three months later you will thank yourself.
- Never cloud-sync the live profile folder. SQLite and cloud sync fight each other, index corruption is the inevitable result. Export first, then cloud-sync the output.
- For multi-account setups: back up once per profile if you use Thunderbird's Profile Manager (thunderbird -P). Each profile is independent.
Frequently Asked Questions
Where does Thunderbird actually store my emails?
Thunderbird stores emails in a profile folder under your operating system user directory. On Windows the default path is C:\Users\USERNAME\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default-release where the random prefix identifies your profile. On macOS it is ~/Library/Thunderbird/Profiles/. On Linux it is ~/.thunderbird/. Inside each profile, emails live in MBOX files under the Mail (for POP3) or ImapMail (for IMAP) subdirectory. The tool either auto-detects this path or you can browse to it manually.
Why not just copy the profile folder as the backup?
Copying the profile folder works for same-version same-OS restores but fails as a long-term archive. The profile bundles Thunderbird-specific SQLite indexes, version-dependent binaries and config formats. Five years from now you may not have a Thunderbird version that opens the profile cleanly. Exporting to open formats like EML, MBOX or PDF makes the backup portable across tools and future-proof. Mozilla itself explicitly says the profile folder is NOT a backup on its own.
Do I need to close Thunderbird before backing up?
Yes. Thunderbird uses SQLite databases (global-messages-db.sqlite, places.sqlite and others) that lock while the app is open. The 4n6 tool can usually read the MBOX files even with Thunderbird running, but you may get partial data on the Inbox and errors on folders being actively indexed. Always fully close Thunderbird before backup, including any background thunderbird.exe processes visible in Task Manager.
What is the difference between MBOX and Maildir in Thunderbird?
MBOX is Thunderbird's default: one flat file per folder, all emails concatenated together. Maildir (optional, disabled by default) stores one EML file per email under a per-folder directory. Mozilla officially warns against Maildir because the implementation has long-standing bugs. If your Thunderbird uses MBOX (most installations do), the backup tool reads those directly. If you have enabled Maildir, exports still work but the tool treats each EML file separately.
Can this tool restore my backup to a new Thunderbird installation?
Not directly. The 4n6 Thunderbird Backup tool is backup-only. To restore a backup into a fresh Thunderbird install: if you exported to MBOX, use the ImportExportTools NG add-on in Thunderbird and import the MBOX files folder by folder. If you exported to PST, install Outlook, import the PST there, then use the 4n6 PST-to-Thunderbird converter or simply add the account to Thunderbird via IMAP and drag-and-drop emails across.
How big is a typical Thunderbird profile?
Typical profiles run 500 MB to 5 GB for light users, 5-15 GB for heavy IMAP users, and 20 GB+ for archive-happy users who keep decades of mail. Attachments are the big driver: a mailbox with lots of image and PDF attachments can easily top 10 GB. Folder compaction in Thunderbird reclaims deleted-email space but is often neglected, so actual profile size is usually bigger than the visible email count suggests.