It takes time, but if you start using the junk controls, the spam will eventually become less frequent. This URL may help: https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages Also, if the spam is coming from the same places, you could set up filters to minimize it. Personally, I also use the mailwasher software. It's free if used for just one account and it works very well if run before starting thunderbird.