Move Thunderbird Profile to New Windows PC

Moving your Thunderbird profile to a new Windows computer transfers all your emails, contacts, calendars, filters, and account settings in one piece. Instead of re-adding accounts and losing local folders, you copy the profile folder and point the new installation at it. This guide covers the full process for Windows 10 and Windows 11.

What You’ll Need

• Access to both the old and new Windows computers
• A USB flash drive, external hard drive, or network share large enough to hold your profile folder (check its size first)
• Thunderbird installed on the new computer (any recent version)
• Your email passwords if you want Thunderbird to remember them (they are not stored in the profile)

Step-by-Step

1. Close Thunderbird completely on the old computer. Click the X on the window, then check the system tray (bottom-right corner, near the clock) for a Thunderbird icon. If it is there, right-click it and choose Exit or Quit. Copying a profile while Thunderbird is running can corrupt the files.
2. Find your profile folder on the old computer. Press Win + R, type %APPDATA%\Thunderbird\Profiles\ and press Enter. You will see one or more folders with names like xxxxxxxx.default. The xxxxxxxx part is a random string of letters and numbers. If you have more than one, note which one is active by looking inside each for a file named profiles.ini in the parent Profiles folder — the active profile is listed under [Profile0] with Path=Profiles/xxxxxxxx.default.
3. Check the size of the profile folder. Right-click the xxxxxxxx.default folder, choose Properties, and note the size. This tells you how much free space you need on your transfer medium.
4. Copy the entire profile folder to your transfer medium. Right-click the folder, choose Copy, then paste it onto your USB drive or external drive. Wait for the copy to finish completely. Do not copy just some files — the whole folder must go.
5. Install Thunderbird on the new computer. Download the installer from the official Mozilla site and run it. You do not need to set up any accounts yet — just complete the installation and close Thunderbird when it opens for the first time.
6. Exit Thunderbird on the new computer. Same as step 1 — check the system tray and quit completely.
7. Locate the new profile folder on the new computer. Press Win + R, type %APPDATA%\Thunderbird\Profiles\ and press Enter. There will be a newly created folder (usually xxxxxxxx.default with a different random string).
8. Replace the new profile folder with your old one. Delete the newly created xxxxxxxx.default folder (or rename it to xxxxxxxx.default.old as a backup). Then copy your old profile folder from the USB drive into the Profiles folder. Make sure the folder name is exactly the same as the one you copied (e.g., a1b2c3d4.default).
9. Update the profiles.ini file (if needed). Open the profiles.ini file in the Profiles folder with Notepad. Look for the line that says Path=Profiles/xxxxxxxx.default. If the folder you pasted has a different name than what is listed, edit this line to match the actual folder name. Save the file.
10. Start Thunderbird on the new computer. Launch Thunderbird. All your accounts, folders, emails, and settings should appear exactly as they were on the old machine.
11. Re-enter email passwords. Thunderbird does not store passwords in the profile folder. When you first connect to each account, you will be prompted for the password. Check the box to save it if you want Thunderbird to remember it.

Common Mistakes

• Copying while Thunderbird is running. This can leave files locked or half-written, leading to a corrupted profile on the new machine.
• Copying only the Mail subfolder. You lose filters, address books, calendars, and account settings. Always copy the entire profile folder.
• Pasting the profile folder inside the default folder. You must delete or rename the new default folder first, then paste your old one as a sibling, not inside it.
• Forgetting the profiles.ini update. If the folder name differs, Thunderbird will not find it and may create a fresh profile.
• Using the same USB drive for other writes during the copy. Interruptions can corrupt the transfer.

Tips

• Use the Migration Assistant add-on (from Mozilla) if you prefer a guided, automated transfer over a network — it handles the copy and path updates for you.
• Keep a backup of the profile folder on the USB drive after the move. It is a handy backup for future troubleshooting.
• If your old profile is very large (many GB), compress it into a ZIP file before copying. This speeds up the transfer and reduces the chance of file-by-file errors. Extract it on the new machine before placing it in the Profiles folder.
• After the move, run Thunderbird’s built-in Help > Troubleshooting Information and check the Profile Folder path to confirm it points to the folder you copied.
• Update Thunderbird on the new computer after the move to ensure you have the latest security fixes.

Troubleshooting

• Thunderbird starts with a blank profile (no accounts). The profiles.ini file likely points to the wrong folder. Close Thunderbird, open profiles.ini in Notepad, and verify the Path= line matches the folder name you copied. Also check that the folder is directly inside Profiles, not nested inside another folder.
• Thunderbird says the profile is missing or cannot be loaded. The folder name may have changed during copy (e.g., “copy of a1b2c3d4.default”). Rename it to exactly what profiles.ini expects, or edit the ini file to match the actual name.
• Emails appear but are empty or truncated. The copy was interrupted. Delete the profile folder on the new machine and copy it again from the USB drive, ensuring the source is intact.
• Passwords are not remembered. This is normal — passwords are stored in Windows Credential Manager, not the profile. Re-enter them once and check “Use Password Manager”.
• Calendar events or address books are missing. These are stored in files like abook.sqlite and calendar-data inside the profile. If they are missing, you likely copied a partial folder — repeat the full copy.
• Thunderbird crashes on startup after the move. One of the profile files may be corrupted. Try starting with thunderbird.exe -P to open the Profile Manager and create a new profile, then copy only the Mail and ImapMail subfolders from your backup into the new profile.

Frequently Asked Questions

Do I need to re-add my email accounts after moving?

No. Account settings (server, port, encryption, folders) are stored in prefs.js inside the profile. As long as you copied the whole folder, all accounts appear automatically. You only re-enter passwords.

Can I move just one email account instead of everything?

Yes, but it is more complex. You would need to copy the account’s subfolder under Mail or ImapMail, plus the associated account settings in prefs.js. For most users, moving the entire profile is simpler and safer.

Will my local folders (Sent, Drafts, Archives) come along?

Yes. Local folders are stored as .sbd directories and files inside the Mail subfolder of the profile. Copying the whole profile preserves them exactly.

What if I already set up Thunderbird on the new computer with accounts?

You can still replace the profile. Close Thunderbird, delete or rename the existing profile folder, then paste your old one. The accounts you set up on the new machine will be lost — only the ones from the old profile will appear.

Is it safe to use a cloud drive (like OneDrive) to transfer the profile?

Yes, as long as you copy the folder to the cloud, then copy it back down to the local Profiles folder. Do not run Thunderbird directly from a cloud-synced folder — it can cause file locking and sync conflicts.

How do I know which profile is the active one if I have several?

Open profiles.ini in Notepad. The section [Profile0] with Default=1 is the one Thunderbird uses by default. The Path= line tells you the folder name.

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