The 'msgFilterRules.dat' file resides in the mail account name folder not in the 'profile name' folder, so it will not be immediately visible when you clickon 'Open directory' * Via 'Menu Bar' toolbar: 'Tools' or via 'Mail Tollbar' toolbar: 'Menu app icon' * Select: 'Help' > 'More troubleshooting information' * Under 'Application Basics' - Profile Directory- click on 'Open directory' this opens window showing contents of profile name folder. * Exit Thunderbird now - this is important. If you use Pop accounts: * click on 'Mail' * click on the pop mail account name folder If you use Imap accounts: * click on 'ImapMail' * click on the imap mail account name folder You can now copy the 'msgFilterRules.dat' file as an extra backup. However, to backup everything, go up the directory to the home folder, you should see the '''.thunderbird''' folder. Then copy the '''.thunderbird''' folder to a suitable location and it contains a backup of everything. I'm assuming you are using the default location. Linux /Unix Profile folders are located here: ~/.thunderbird/<Profile name>/ However, if you're using a third party build from Debian or Ubuntu, those builds store your profile folder here: ~/.mozilla-thunderbird/<Profile name>.