How To Fix Thunderbird Letting in Too Much Junk Email

Thunderbird has starred letting in far too much junk email recently and the spam filters are not doing their job. I set about finding a fix.

By doing the "Mark as Junk" menu action, you are telling the spam filter to read the emails and remember certain details so that when another comes in similar, it can recognise it as spam. This is an adaptive learning program.

The trouble is that after a while, it becomes less and less effective at picking up on my spam emails, and I have to repeatedly mark them as junk on the same emails coming in.

Does this problem sound familiar? Well, there is a solution, and it's really simple.

When you installed Thunderbird and marked a few junk emails as spam, the algorithm worked from a clean slate. As you add more and more junk emails as spam, the data grows and grows. Fast forward half a year or so, and your junk email recognition software has the details of all the spam emails sent to you in the past six months, but guess what? If you could pull back an old spam email and compare it with one from today, you would see that they are completely different in structure and wording. Your junk email filter rules are based on yesterday's junk email, not today's.

Junk Email Evolves

As more sophisticated spam filters emerge, writers must use more sophisticated techniques to get past them. It's a constant battle between the two sides, with one leading for a while, then the other.

The simple solution to the problem is to reset the Thunderbird junk email training data. This wipes out all the data from the past six months (or however long since you installed Thunderbird) and lets you start blocking spam from today's junk email senders without the data being polluted with old spam.

Here's how to do it.

1. Open up Thunderbird if it isn't already open
2. On the Tools menu select Options
3. On the Privacy tab select Junk
4. Click on the button that says "Reset Training Data"
5. Done!

OK, so you have to retrain Thunderbird for a few days or so, but afterwards, it will be much more efficient at picking up and blocking spam emails, and you won't have to keep marking the same emails as spam.