How do I get senders that I've marked as spam to end up in the spam folder thereafter?

In this excerpt from
Answercast #83, I look at various spam filtering techniques and ways to
teach programs to handle spam.

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Getting spam into the spam folder

The short answer is no. Spam is ubiquitous; we are dealing with it to varying degrees successfully and otherwise.

What I would caution you about is assigning too much importance to the sender of a piece of spam.

Spammers regularly spoof, falsify, and change the sender of spam messages that they send. In other words, you may get five copies of the same piece of spam from five different people. You may see five different names – and the email addresses associated with those five different names have no relationship to those names at all.

Train you spam filter

Spammers are doing everything that they can to, not only to confuse you, but to bypass the spam filters. The best thing you can do as an individual fighting spam is to train your spam filter.

In Outlook, that means when you find a piece of spam in your inbox mark it as “spam” or “junk,” depending on the term that the program happens to use.

Make sure that junk mail filtering is enabled in your options. That way, over time, Outlook will learn what it is that you consider to be spam – and it will automatically then send any email that looks like what it has learned into the spam folder.

False positives

Now, I do have to caution you (and this is true for Outlook and for any other spam filtering technique) – periodically have a look at your spam folder. The problem is that spam-fighting techniques can occasionally result in what are called “false positives.” In other words, email that you actually want that is filtered as spam.

The thing to do is, when you find such a piece of email in your junk mail folder, mark it as “Not spam.” Mark it as “Not junk.”

That’s just as important in training the Outlook spam filter as marking “spam” to begin with. This tells the spam filter, “This thing over here that you marked as junk – it’s not. Learn from that.”

So, the best way to approach spam is to simply make judicious use of your spam filters in whatever email program you happen to be using. Outlook has a good one. Thunderbird has a good one. On the web, I personally find Gmail’s spam filter to be one of the best.

(Transcript lightly edited for readability.)