What is the best way to archive Thunderbird emails?

Four completely different jobs get called archiving, and picking the wrong one is how people lose mail.

Clicking the Archive button does not back anything up. Copying your profile folder does back everything up, but the result is only readable by Thunderbird, which is cold comfort on the day Thunderbird is the thing that broke. Neither of those is what a compliance officer means when they ask for an archive.

Which means the question worth answering is not which method wins. It is which of the four jobs you have in front of you.

Quick answer. For everyday storage, install the ImportExportTools NG extension and export folders to EML or MBOX. For a full safety copy, close Thunderbird and copy the whole profile folder. For anything legal or regulatory, export to PDF with headers intact. Do the profile copy first regardless, because it takes two minutes and it protects you while you decide on the rest. All of this works the same on macOS and Linux apart from where the profile folder sits.

Does the Thunderbird Archive button back up your email?

No. Not in any sense that would help you on the day you need it to.

The Archive button moves messages out of your Inbox and into an Archives folder. That folder lives in the same profile, on the same disk, inside the same MBOX files. If the profile corrupts, the archived mail corrupts along with everything else, and if the drive dies then the Archives folder dies at precisely the same moment as the Inbox it was supposed to be protecting.

It is a filing feature, and a decent one. A good one, and the folders it makes are genuinely useful for keeping an Inbox navigable, but calling it archiving in the backup sense has cost people their mail more than once.

You'll find the setting under Account Settings and then Copies and Folders, where the checkbox reads Keep message archives in. Turn it on if you want tidier folders. Don't count it as a copy of anything.

How do you back up the Thunderbird profile folder?

This is the two minute job everybody should do before anything else, and the one most people put off until the week after it would have saved them.

Everything Thunderbird knows about you sits in one directory. Mail, folder structure, address book, calendars, saved passwords, filters, extensions, account settings. Copy that directory and you have copied the lot.

Finding it is easier from inside the app than by hunting through AppData. Open the menu, choose Help, then More Troubleshooting Information, and under Application Basics click Open Folder. Thunderbird opens the profile directory for you. On Windows it sits under %APPDATA%\\Thunderbird\\Profiles in a randomly named directory ending in .default-release, which is exactly why the menu route is less painful.

Then three rules, and the first one is not optional.

● Close Thunderbird completely before you copy. Copying a profile mid write gives you a half consistent snapshot and you will not find out until you try to restore it

● Copy the entire folder, not selected pieces. The parts that look like junk are not junk

● Put the copy somewhere that isn't the same drive, because a backup on the failing disk is not a backup

Restoring is the reverse. Drop the folder back in place on the new machine, point Thunderbird at it, and everything comes back including the account passwords you had forgotten you ever set.

The limitation is the part people skip past. A profile backup is only useful to Thunderbird. So if the reason you are reading this is that Thunderbird will not open, or the machine it lived on has already been wiped and handed to somebody else, or the destination is Outlook and Outlook has never in its life understood MBOX, then a folder full of extensionless files has not actually solved your problem. It has only preserved it.

What is inside the Thunderbird profile folder?

Worth knowing, because it explains several of the things that go wrong later and turns them from mysteries into ordinary problems.

Your mail sits in files with no file extension at all. A folder called Inbox is the actual Inbox, holding every message you have ever received as plain text in MBOX format, one after another, separated by nothing more sophisticated than a line beginning with the word From.

Next to each one sits a matching .msf file. Those are summary indexes, not mail. Thunderbird builds them to know what's in each MBOX without reading the whole thing, and they are the single most common source of confusion during recovery, because they go out of sync with the underlying mail. When a message vanishes from the Thunderbird interface but the bytes are still on disk, a stale .msf is usually the reason.

Nested folders live in .sbd subdirectories, which is why deleting something that looks like a stray directory occasionally takes half a mailbox with it. Worth noting that Thunderbird can also be configured to use Maildir instead of MBOX, storing one file per message rather than one file per folder, though almost nobody switches and the default has stayed MBOX for two decades. So a folder called Projects with subfolders produces a Projects file and a Projects.sbd directory sitting beside it.

One historical wrinkle. Older Thunderbird builds struggled with MBOX files past 4 GB because of 32 bit file size limits, which is why an ancient Inbox that has never been split is worth exporting rather than leaving to grow.

Should you move mail to Local Folders before archiving?

This is the missing middle step, and it solves the IMAP problem the other methods dance around.

Mail in an IMAP account is not really yours in the local sense. Thunderbird holds a cached copy and the server holds the real one, so anything you archive from an IMAP folder is archiving a mirror. Delete it server side later and your local copy may follow it.

Local Folders is different. Mail placed there lives on your disk and nowhere else, which is exactly what you want before archiving anything.

A pattern Mozilla forum regulars have recommended for years works like this. Create an Archives folder inside Local Folders. Point the archive settings at it, choosing yearly or monthly subfolders. Then archive, and Thunderbird builds a tidy structure of Archives, then 2025, then 2025-01, then Inbox and Sent inside it.

That gives you small organised files rather than one enormous Inbox, which makes both backup and later recovery far less painful.

If you'd rather not use the archive settings at all, synchronise your folders, switch Thunderbird to offline mode so nothing syncs while you work, then highlight the messages and use Copy To rather than Move To. Copy leaves the server copy alone until you decide otherwise.

Should you compact folders before you archive?

Nobody mentions this and it changes what your archive actually contains.

Deleting a message in Thunderbird does not remove it from the MBOX file. It gets marked as deleted and stays on disk, still taking space, still sitting inside the file you are about to copy. Compacting is the operation that actually removes them, and it works by writing a temporary NSTMP file containing everything still live, then replacing the original MBOX with it.

Two consequences worth knowing.

Archive before compacting and your archive includes messages you thought you had deleted years ago. That is either a nice surprise or a compliance problem, depending entirely on what your organisation has committed to in writing.

Compact before archiving and those messages are gone permanently. Not recoverable. So run the profile folder copy first, then compact, then archive, in that order, and you have both versions.

One genuine danger sits nearby. The disk space recovery options under Synchronization and Storage can delete old messages from the IMAP server rather than only from your local cache. Mozilla's own Bugzilla carries reports from users who lost close to a decade of mail this way. Read that dialog slowly, and never touch it before your profile backup exists.

How do you export Thunderbird emails to readable files?

With an extension, because Thunderbird has no export function of its own and never has.

That surprises people every time. There is no File then Export in Thunderbird, there never has been, and the number of forum threads that begin with somebody hunting for it suggests the omission has outlasted several redesigns. What everyone uses instead is ImportExportTools NG, free from Mozilla's own extension directory, and it has been the standard answer for years.

Install it from the Thunderbird add ons site, restart, then right click any folder and the ImportExportTools NG menu appears. It works the same way in Betterbird, SeaMonkey and Postbox, since the forks share the profile format. Export Folder writes the whole thing. Export All Messages In The Folder lets you pick the format. Right click an account rather than a folder and Export All Folders does the entire tree in one go.

Formats worth knowing.

EML gives you one file per message, with attachments intact, openable by Windows Mail, Outlook, Apple Mail and most other clients. Each one is a plain RFC 5322 message, which is the same thing that travelled across the internet in the first place. Linux forum threads have been pointing people at EML for a decade now, and it remains a sound default for personal archiving.

MBOX bundles a whole folder into a single file, which keeps things tidy and imports cleanly into Thunderbird, Apple Mail and anything else Mozilla shaped.

HTML produces something any browser opens, which matters if the person who inherits this archive is not technical. CSV is there too when what you actually want is a spreadsheet of senders, subjects and dates rather than the messages themselves, and plain TXT when the archive is destined for a search index or a grep rather than a human.

PDF is the format to pick when the archive might be read by a lawyer, an auditor or a court.

The catch is that the extension needs a working Thunderbird to run inside. If Thunderbird launches fine, this is your answer and it costs nothing. If it doesn't, keep reading.

Is MailStore Home a good way to archive Thunderbird mail?

Worth knowing about, and free for personal use.

It builds a central searchable archive across Thunderbird, Gmail and other accounts rather than exporting files into a folder. Search is fast, restore back into Thunderbird works, and for somebody consolidating a decade of mail from three different clients and two dead laptops it does a job that a folder of exported files simply cannot.

The tradeoff is that you've moved your archive into another application's storage format. That's fine while MailStore exists and you're still on Windows. It's the same dependency you had with Thunderbird, wearing a different hat.

What breaks when you archive Thunderbird emails?

Four failure modes come up repeatedly. Three of them have free answers.

The profile is locked. Thunderbird writes a parent.lock file when it starts and removes it on a clean shutdown. Crash it, or leave a process running invisibly, and the lock stays. Open Task Manager, end the process, and try again. A reboot handles whatever that misses.

Messages have vanished from the interface. Right click the folder, choose Properties, then Repair Folder. That rebuilds the .msf index from the underlying mail, and in most cases the messages reappear because they never left the MBOX file in the first place.

Support engineers report reproducing this on Thunderbird 91, 102, 115 and 128 ESR alike, so treat it as a recurring behaviour rather than a bug in any one release. The usual causes are a stale index after a crash, a filter quietly moving mail into Trash or Junk where nobody thinks to look, antivirus interfering with the profile, or an IMAP account that stopped syncing because a password changed or the server quota filled up. For the IMAP case specifically, open Account Settings, go to Synchronization and Storage, and confirm that keeping messages on this computer is enabled, because without it Thunderbird is only ever showing you a cached view of the server.

The MBOX file is enormous. Export in pieces rather than all at once, scoping by folder or by date range, since a single job on a 40 GB profile is where timeouts and half finished exports come from.

Thunderbird will not launch at all. This is the one with no free answer, and it's also the most common reason anyone searches for this in the first place. Every method above assumes a working Thunderbird. Repair Folder needs it. ImportExportTools NG runs inside it. MailStore reads through it.

When the app itself is the broken component, you are left holding a directory of nameless files that nothing on the machine will open.

How do you archive when Thunderbird is gone?

Same underlying problem, three shapes it usually arrives in. Orphaned profile from a machine that was retired. Profile copied off a dead drive with no install anywhere. Or Thunderbird still installed but refusing to start.

The mail is intact in all three. That is the thing worth holding on to. MBOX is plain text and the messages are sitting there in readable form. What's missing is something that reads MBOX bytes without needing Thunderbird's cooperation.

Any tool that does this should meet four conditions before you trust it with the only copy of anything.

● Reads MBOX directly rather than driving Thunderbird behind the scenes

● Opens the profile without needing the lock released

● Ignores the .msf indexes and reads the underlying mail, since stale indexes are the thing hiding your messages

● Shows you what it found before it writes anything

That last one matters more than the feature list. You want to see the folder tree and click into actual messages before committing, because that's how you catch a partial parse while you still have options.

How do you archive Thunderbird emails for legal retention?

Different requirement, different output, and the gap between the two catches people who assumed a folder of EML files would satisfy a regulator.

If this archive exists because of a retention policy, a legal hold or a regulator, then readable files are not enough on their own. What auditors ask for is typically PDF or PDF/A with the full message headers preserved rather than just the visible body, because the headers are what establish who sent what and when. A hash log alongside the export supports chain of custody, which is what HIPAA and GDPR retention programmes tend to want evidence of rather than just the files. And the source needs to be read without modification, which rules out anything that opens the profile in write mode.

ImportExportTools NG produces PDF and covers a fair number of these cases. Where it falls short is the header fidelity and the audit trail, so check what your actual obligation says before assuming either way.

Frequently asked questions

Is copying my Inbox file to a USB stick enough?

You can, and it's better than nothing, but you'll be missing the .sbd subdirectories holding your nested folders and everything outside that one file. Copy the whole profile instead.

Do I need to copy the .msf files?

Not really. They're rebuildable indexes rather than mail. Copying the whole profile brings them along anyway and that's simpler than being selective.

Will my archived emails still have attachments?

Yes, in every method here. EML and MBOX both carry attachments inline as MIME parts. PDF embeds or lists them depending on the tool.

How often should I do this?

Profile copy monthly if the mail matters, and always before a Thunderbird major version upgrade or an operating system reinstall. Those are the two moments things actually go wrong.

Can I archive from an IMAP account?

Yes, though be aware IMAP mail lives on the server and Thunderbird only holds a synchronised copy. POP accounts are the opposite case, since the mail is already local and the server may have nothing left on it. Drag the messages into Local Folders first, which makes them genuinely local, then archive that.

Does archiving delete the original email?

Nothing, unless you delete it yourself. Archiving copies rather than moves in every method described here, except the built in Archive button, which moves messages between folders inside the same profile.

Should I compact folders before archiving?

Profile copy first. Compact second. Archive third. Compacting permanently removes messages that were marked deleted but still sitting in the MBOX file, so doing it first means they never reach your archive.

Is MBOX or EML better for archiving?

EML if you want individual messages you can open, search and forward one at a time. MBOX if you want folder level files that import cleanly back into a mail client. Plenty of people keep both, since disk is cheap and the two formats fail differently.

Picking a method and checking that it worked

Copy the profile folder today. Right now, ideally. It takes two minutes, it needs no software, and it covers you while you work out the rest.

Then pick based on what the archive is for. Keeping it inside Thunderbird means the built in Archive folders are fine. Wanting files you can open in ten years means ImportExportTools NG to EML or MBOX. Facing an auditor means PDF with headers and a record of what was exported.

Whatever you choose, verify it. Open five random messages from the archive and check the attachments open. An unverified backup is a guess wearing a reassuring name, and the moment of discovery is never convenient.

One case sits outside all of that. If Thunderbird won't launch, or the profile came off a machine that no longer exists, none of the free routes apply, because every single one of them runs inside the app you no longer have.

PCDOTS Thunderbird Converter exists for that case. It's Windows software, so if your dead profile is sitting on a Mac or a Linux box, copy the folder onto a Windows machine first. The profile format is identical across operating systems, so the bytes read the same wherever they were written.

Point it at the profile folder and the first thing you get is the folder tree. Click into messages. Check the ones you were worried about. It reads the MBOX bytes directly without needing a Thunderbird install, ignores the .msf indexes that hide messages, and opens profiles that are still locked because it never asks for the lock in the first place. The read is one way only, so nothing is written back to your source.

Then export. Most people want PST if they're heading to Outlook, or PDF if this is going to a lawyer. MBOX, EML, MSG and direct delivery into Microsoft 365 or Gmail are all there when you need them, and none of it is a decision you have to make before you've seen your mail.