16 September 2026 · 5 min read

Back up and restore Thunderbird Local Folders

Back up Thunderbird's active profile and any Local Directory stored outside it with Thunderbird closed. Test the backup in a separate profile before replacing or removing working mail.

Thunderbird Local Folders can contain mail that exists nowhere on a server. Adding the same email account on a new computer will not bring those messages back. A useful backup must include the actual message storage and a way to check that it can be restored.

Do you want a profile backup or a portable mailbox?

Copy type	What it is useful for
Complete profile backup	Restoring Thunderbird accounts, preferences, address books, and mail stored inside the profile.
Mailbox export	Reading selected mail in another compatible application or preparing an Outlook conversion. It does not recreate all Thunderbird settings.
External Local Directory copy	Preserving mail deliberately stored outside the profile. Keep it alongside the profile backup and note its original location.

A profile is Thunderbird's working data directory. Local Folders is a mail location shown inside Thunderbird. They are related, but their names do not prove that every message lives inside the profile directory.

Find the folders that actually contain your mail

Open Account Settings → Local Folders and record the Local Directory path. Check other accounts' storage paths too if the backup needs their local mail. A customized path may point to another disk or directory. Mozilla describes this setting in its account configuration reference.

Then open Help → Troubleshooting Information and use the Profile Folder or Profile Directory button to locate the active profile. Using the application avoids guessing which of several similarly named profiles is in use. Record both paths before closing Thunderbird.

For example, the active profile might be on the system drive while Local Folders points to a separate mail drive. Copying only the profile would preserve the setting that points there, but not the external mail itself. Check that each recorded message-storage path is either inside the copied profile or included separately.

Create the backup while Thunderbird is closed

For a small profile, Thunderbird offers Tools → Export. Its built-in ZIP export currently supports profiles up to 2 GB; Mozilla directs larger profiles to a manual file copy. See Mozilla's export instructions.

For a manual backup:

Close Thunderbird completely after locating the active profile and message directories.
Copy the complete profile directory into a new, dated backup folder.
Copy any external Local Directory into a separate subfolder, keeping its internal structure intact.
Add a short text note with the Thunderbird version, original paths, backup date, and what the copy includes.
Keep a second copy on separate storage after the first copy finishes successfully.

Do not merge a new backup into an old one when you cannot tell which files will be replaced. A separately dated copy is easier to restore and compare. A cloud-synchronized working profile is also different from an independent backup: synchronization can propagate unwanted changes.

Which files matter in an MBOX store?

First check Message Store Type in the relevant account settings. With File per folder (mbox), a mailbox such as Inbox often has no extension, its .msf companion is an index, and a matching .sbd directory holds nested folders. Keep the mailbox and its nested structure together.

A File per message (maildir) store has a different layout. Do not rename it or feed the directory to an MBOX converter. The complete-profile backup route avoids having to guess which individual files are needed. Mozilla explains the MBOX/Maildir distinction.

For a portable MBOX export, use a compatible mailbox export tool and verify the exported folders separately. If the next destination is Outlook, follow the Thunderbird-to-Outlook guide after safeguarding the full source.

Test restoration without overwriting the working profile

Use a separate Thunderbird profile for the test. Mozilla's Profile Manager instructions explain how to create and select one. Keep the working profile and backup untouched.

Disconnect the computer from the network before importing the backup or opening a restored profile for the first time. This prevents restored live accounts from synchronizing during the initial local-mail test.

In the test profile, open Tools → Import. For a Thunderbird backup ZIP within the supported size, choose the file import route. For a larger copied profile, choose Import from another Thunderbird installation, then Choose a profile folder. Review the data selection before starting. These are the routes in Mozilla's import documentation.

Check any external Local Directory especially carefully. If a restored configuration still points to the original mail drive, viewing its messages does not prove that the backup contains them. Make a separate working copy of the backed-up external directory. In the test profile, open Account Settings → Local Folders → Local Directory → Browse and select that working copy. Restart Thunderbird and confirm the selected path before inspecting messages. Do not select the original mail directory or your only backup copy.

Keep the computer offline during this inspection. Open known old messages, nested folders, and attachments from the restored data. Check the storage paths as well as the message list.

What does a failed restore tell you?

Result	Likely next investigation
Account settings return but Local Folders are empty	Recheck the external Local Directory and whether its files were copied.
Main folders return but subfolders do not	Compare the original and backup directory trees, including nested mailbox storage.
Subjects appear but attachments will not open offline	Confirm the source stored full messages, not just downloaded headers or an incomplete cache.
The import tool rejects a ZIP	Check its size and whether it is a Thunderbird profile export rather than an unrelated mailbox ZIP.

Keep a note of which test profile was used and which backup paths it read. Once you can reproduce the needed mail from those copies, store the backup safely. Restore success should not depend on the old computer's original mail directory still being available.

Primary sources

FAQ

Does a profile backup always include Local Folders?

Only if their message storage is inside that profile. Check Local Directory and separately copy any external mail-storage directory with Thunderbird closed.

What if the profile is larger than 2 GB?

Mozilla documents a 2 GB limit for the built-in ZIP export/import route. Copy the closed profile manually and use the profile-folder import option when restoring larger profiles.

Can signing in on a new computer restore Local Folders?

No. Signing in downloads server mail, not local-only folders from the old computer. You need the saved local message data.

How do I know I tested the backup rather than the original?

Check the test profile and Local Directory paths. They must read separate working copies of the backed-up data, not the original mail directory or your only backup copy.

Keep reading

Moving the backed-up mail into Outlook?

Choose a transfer route that fits your source and destination.

Read the Thunderbird migration guide Ask support