I doubt that there is any way to sync the filters themselves. In each Thunderbird installation the filters are stored as files named msgFilterRules.dat: it would be a complex task to keep all those files the same across several machines. In your shoes I'd be looking to use server capabilities instead. One option is simply to use the spam filter offered by your mail provider. I have a mail account with Yahoo for example, and I let them identify messages as spam: I don't filter that account in Thunderbird. But I do subscribe to their 'spam' folder in Thunderbird (as well as the Inbox etc.) so I can review how they classify the mail. They don't catch all the spam but my experience is that they get most of the obvious stuff, the rest I can flag myself. The other option would be to let '''one''' of your Thunderbird machines do the filtering and move spam into a folder on the account. If that folder is subscribed to the server, and all the other machines access it, then you could see those messages from them all. That way you only have one set of filters to maintain, and you can tweak them and make them as complex as you like.