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Thunderbird Message Filters

Carry your existing message filters across to your upgraded mailbox.

When you add your upgraded mailbox to Thunderbird it is set up as a brand new account, so any message filters you had created are left behind on the old account. Thunderbird has no built-in way to copy filters between accounts, but the filters are stored in a single file that can simply be copied across.

This guide assumes you have already added your mailbox with the new server settings, following our Mozilla Thunderbird setup guide, and that the previously configured account with the old server settings is still present in Thunderbird. You need both accounts in place to complete these steps.

Copying your filters

Both accounts store their filters in a file named msgFilterRules.dat, each in its own folder on your computer. The first few steps locate those two folders.

  1. In Thunderbird, right-click the old account in the folder list, and choose Settings.
  2. Click on Server Settings beneath the same mailbox, then triple-click the Local Directory text box to select all of the text in it.
  3. Press Ctrl-C to copy the path to the clipboard.
  4. Open File Explorer, paste the path into the address bar, and press Enter to open the folder.
  5. Repeat steps 1–4 for the new account. You should now have two File Explorer windows open, one showing the folder for the old account and one showing the folder for the new account. Both should contain a msgFilterRules.dat file.
  6. Close Thunderbird — otherwise it will overwrite the changes you are about to make when it next saves your filters.
  7. In the folder for the new mailbox, rename msgFilterRules.dat to msgFilterRules.bak, to keep it as a backup.
  8. Copy msgFilterRules.dat from the old mailbox folder into the new mailbox folder. Take care to do this the correct way around — the file is being copied from the old account to the new one.
  9. Open Thunderbird again. Your filters should now be in effect on the upgraded mailbox.

To check the filters have come across, right-click the new account, choose Message Filters, and confirm your filters are listed. Filters that move messages into a folder will need that folder to exist on the upgraded mailbox, so it is worth opening each filter to confirm the destination folder is still set correctly.