Exporting and Importing Thunderbird Message Filters

Thunderbird stores message filters in per-account configuration files, making it inconvenient to replicate filters across multiple accounts or installations. Rather than recreating filters manually, you can copy filter files directly or use symbolic links to keep filters synchronized.

Where Thunderbird Stores Filters

Thunderbird saves filter rules in msgFilterRules.dat, a plain text configuration file. Each account maintains its own copy in its local mail directory. On Linux, your profile location is ~/.thunderbird/.

Find all filter files across your profile:

find ~/.thunderbird/ -name msgFilterRules.dat

Output typically shows:

~/.thunderbird/[profile-hash].default/Mail/Local Folders/msgFilterRules.dat
~/.thunderbird/[profile-hash].default/Mail/[account-name]/msgFilterRules.dat

Account-specific filters live in their respective mail directories. The Local Folders filter file can serve as a central source for distributing filters to multiple accounts.

Backing Up and Copying Filters Between Accounts

Before making any changes, close Thunderbird completely. Thunderbird rewrites msgFilterRules.dat on exit, so any manual edits while the application runs will be lost.

To copy filters from one account to another:

# Close Thunderbird first
cp ~/.thunderbird/[profile].default/Mail/[source-account]/msgFilterRules.dat \
   ~/.thunderbird/[profile].default/Mail/[dest-account]/msgFilterRules.dat

Replace [profile], [source-account], and [dest-account] with your actual profile hash and account names.

If your filters reference custom headers, also copy that setting from prefs.js:

grep mailnews.customHeaders ~/.thunderbird/[profile].default/prefs.js

Add the output to the destination profile’s prefs.js if the setting doesn’t already exist.

Using Symbolic Links for Unified Filters

For a cleaner approach that keeps all accounts synchronized without manual duplication, use symbolic links. This way, editing filters in one place affects all linked accounts.

Choose a source filter file (Local Folders works well if you don’t use it for mail storage):

SOURCE="$HOME/.thunderbird/[profile].default/Mail/Local Folders/msgFilterRules.dat"

For each account that should use these filters, replace its filter file with a symbolic link:

cd ~/.thunderbird/[profile].default/Mail/[account-name]/
ln -bsv ../../Mail/Local\ Folders/msgFilterRules.dat msgFilterRules.dat

The -b flag backs up the original msgFilterRules.dat as msgFilterRules.dat~ before creating the link, preserving your previous configuration.

Verify the links are in place:

ls -la ~/.thunderbird/[profile].default/Mail/*/msgFilterRules.dat

All symlinked accounts now reference the same filter file.

Restoring Symlinks After GUI Edits

When you edit filters through the Thunderbird GUI (Message → Filters and Search → Mail Filters), Thunderbird may replace the symlink with a regular file. After making filter changes, verify your symlinks:

ls -l ~/.thunderbird/[profile].default/Mail/[account-name]/msgFilterRules.dat

If a symlink was replaced with a regular file, restore it:

rm ~/.thoroughbird/[profile].default/Mail/[account-name]/msgFilterRules.dat
ln -bsv ../../Mail/Local\ Folders/msgFilterRules.dat msgFilterRules.dat

Restart Thunderbird to reload the filters.

Direct Editing of Filter Files

The msgFilterRules.dat file is plain text and can be edited directly while Thunderbird is closed. This is useful for bulk modifications, merging filters from multiple sources, or version control.

Each filter rule follows this structure:

[num1]
name=Filter Name
enabled=yes
account=account-name
action=copy
actionValue=/path/to/folder
condition="Subject contains test OR From contains example@example.com"

Always back up before manual edits:

cp msgFilterRules.dat msgFilterRules.dat.backup

Edit with your preferred text editor:

vim ~/.thunderbird/[profile].default/Mail/[account-name]/msgFilterRules.dat

Common filter actions include:

• action=copy — Copy matching messages to a folder
• action=move — Move matching messages to a folder
• action=delete — Permanently delete matching messages
• action=mark — Mark messages as read, flagged, or with a tag

Conditions support boolean logic with AND, OR, and NOT operators:

condition="(Subject contains Invoice) AND (From contains @company.com)"

Syncing Filters Across Multiple Machines

For different machines, copy the filter file via SSH:

scp user@remote-machine:~/.thunderbird/[profile].default/Mail/Local\ Folders/msgFilterRules.dat ~/

Then import using the backup-and-copy method described earlier.

For multiple profiles on the same machine, replicate the symlink approach for each profile directory.

Troubleshooting

If filters don’t appear after importing, check:

• The destination account folder exists
• Thunderbird was closed before copying files
• File permissions are readable by your user
• The folder paths in filter actions exist and are accessible

Restart Thunderbird after any manual changes to msgFilterRules.dat. The application caches filter rules in memory, so it won’t recognize direct file edits until restart.