It took me a while to understand you are not talking about spam at all. You are asking about filters in general. They are completely different things and to be honest I feel any attempt to manually menage spam with filters is destined to complete failure but will consume inordinate amounts of time. Each mail account maintains a msgfiltersrules.dat file within it account folders in your profile With careful editing these text files can be bulk updated using a basic text editor (not a word processor) The first criteria is Thunderbird must not be running in any way when you are meddling in the profile folder. Bad things hempen if it is. The second thing is make plenty of backups because as I said careful editing, that means there is lots that can go wrong. But if you change one and save it and copy the change in a find and replace you should get the outcome you seek. But remember find and replace will replace every instance it sees of that text string. SO backup so you can recover if it does not work how you expect. A full profile backup might be germane, as messing up filters can mess up stored mail in a folder you apply it against.