How the Spam Fighters program works

Over here in (and Office 365), we hate spam (and phishing, and malware). We're doing everything we can, every single day, to keep it out of your Inbox.But we know that there are many of you out there as well that also hate spam as much as we do, and that's where the Spam Fighters program comes in.

Most of you reading this will have no idea what this "Spam Fighters" program is. So, for those of you who don't know what it is, and the few of you who do, here's a rundown.

You may already be familiar with Smartscreen, the spam filter that powers but also is used in other Microsoft products like Edge (the new web browser in Windows 10). Smartscreen works by machine learning, and it's been machine-learning before the term "machine learning" was a buzzword in the industry.


In order for Smartscreen to be both predictive and effective, it has to learn on a corpus of good and bad email. While we can always find sources of spam (through honeypots and user feedback reports), it can be difficult to acquire a corpus of good email. That's where the Spam Fighters program comes in.

The Spam Fighters program asks a random sample of users in if they'd like to volunteer to help fighting spam. These invitations are sent periodically, and they are randomly sampled in order to get a good cross-section of users. If you agree, then each day at most we'll send you a copy of an email that was meant for you and ask you to grade it - Is it spam? Or non-spam?

This is all down-sampled from your own email stream, you aren't looking at anyone else's email. You take a look at it, and vote on what you think it is. There is a little wrapper at the top of the message that contains a banner letting you know what the message is, the voting buttons, and then the Not junk and Junk buttons.

Below is an example:


These are all messages that were already sent to you, they are not held up waiting for you to vote.

When you do vote:

  1. First, your choice of spam or non-spam is record for that particular message
  2. Your choice is then compared to what the spam filter said for that message when it was scanned through the filter:
    a) Did you say it was spam and the filter agreed? Then everything is good
    b) Did you say it was non-spam and the filter agreed? Then everything is good
    c) Did you say it was spam but the filter said it was non-spam? Then we have a false negative (missed spam)
    d) Did you say it was non-spam but the filter said it was spam? Then we have a false positive (good email classified as spam)
  3. Your vote is then compared against the votes of all other users receiving similar email. Does everyone overwhelmingly agree with you? Or disagree with you? Or are the votes split up?

These votes from all the users across the entire Spam Fighters program are combined, and the messages combined to create a corpus, and then Smartscreen learns across numerous features within a message - sending IP, sending domains, authentication status, headers, body of message, attachments, encodings, and so forth. This feeds into our IP reputation, and into the Smartscreen spam filtering algorithm. This algorithm is what does the filtering for spam, malware, and phishing as well as legitimate email. It's updated multiple times per day.

So, by participating in the Spam Fighters program and voting on a regular basis, you really are helping to fight spam, and your vote counts!

Your email is downsampled and the Spam Fighter vote only happens at most once per day, but it also depends on your email stream so it may not happen every day. But the key point to remember is that machine-learning depends on random sampling.


This means that even though your email is downsampled, Spam Fighter voting does not keep a history of the previous message that was sent to you. Thus:

  • It is entirely possible that you may get two similar, or even identical messages, in a row. Or more.
  • We're not asking for you to vote on messages because we don't know whether or not it's spam. Sometimes we do know, sometimes we don't. Rather, we're building a cross-section of email that is representative of the entire user base, and using that to train on a corpus of labeled messages..
  • Similarly, it's entirely possible that legitimate messages will end up in the Spam Fighters program, asking you to vote on it. "Don't you know that's my Amazon newsletter?" Or "This is a message from Microsoft! How can you not know whether or not your own email is spam or not?!" But here again, we're looking to learn from a representative section of all email, legitimate or not, bulk or not, newsletter or not, transactional or not, or whether it's from Microsoft or not. It's important that even newsletters get into the training system.
    Remember that machine learning is based upon random sampling, and by artificially bumping up or down certain types of messages, that changes the way the filter operates and makes it less accurate in the future..That's also why you can't volunteer for the program. Users in it are selected at random, and participation is entirely voluntary. You can opt-out at any time by clicking the "stop participating" link in the email (although you can also just ignore the email from time to time if you're busy  but still want to participate in the fight against spam). You really are helping.
  • When you vote Spam or Not spam, this is not directly tied to the equivalent message in your Inbox. That is, if a spam is in your Inbox and you get a Spam Fighter email that sampled that exact spam, clicking "Spam" in the Spam Fighter email doesn't report the message as spam back to us, nor does it add to Blocked Senders, nor does it move the original message out of your Inbox and into Junk Email if you hadn't yet moved or deleted it (the reverse is also true for clicking "Not spam" if the message was originally detected as spam).
    Instead, your vote is recorded and used as an input for future messages. In order for you to rescue a message (for false positives) or remove it from your Inbox (for missed spam), you'll need to use the regular UX tools.

That's an overview of the Spam Fighters program in For those of you involved in it, we thank you for your participation.


Comments (11)
  1. Matthew says:

    Good read, Terry. I’d not heard of this program. Are there any plans to include this in Office 365?

    1. tzink says:

      We developed a version in Office 365 a couple of years ago, but it never really took off. There’s a lot of requirements for legal opt-in, users didn’t like being asked to grade their email, and it undermined the entire premise of random sampling.

      So, in my view, the chances of its expansion in Office 365 are small.

  2. Rafael Viana says:

    In my opinion the way that this Spam Fighter is presented to the mailbox owner (users) doesn’t reflect the entire purpose of the program. The idea is to fight spam but it asks the users if they think that it is “junk”, which might lead the user to a decision that might not reflect the intention of this program. Most people don’t event know what spam is exactly and they often mark a message as spam when they actually wanted the message to not apear in their inbox and go to a “promotions” tab or simply unsubscribe.

    What I’m trying to say is that the the way that that this is presented to the reader should explain the consequences (as stated here in this blog post), and the sample size shouldn’t be this small as it has a great impact on the senders even if they are doing email marketing properly but are being punished by a misleading question that is made by a subset of people.

    1. MArrow says:

      I totally agree with you

  3. Pascal says:

    Hello Terry,
    it looks like a SRD (Sender Reputation Data) evolution.
    That would be great to provide data to senders as Return Path certification program does

  4. Terry says:

    I find emails in junk that I did not mark as junk or spam, is there a difference between Junk and Spam?

    1. tzink says:

      Junk and Spam are the same thing, I use the two terms interchangeably.

  5. Matthew says:

    And does this information get put into the Complaint Feedbackloops for ESPs? Just curious.

  6. StephenB says:

    Great. Now perhaps you could also do something about the huge volume of SEO & web development spam that comes FROM the & Hotmail servers? Or at the very least, maybe you could stop ignoring spam complaints and actually start canceling spammer accounts? Just a thought…

  7. B Freem.... says:

    Trying a second posting. Not sure if my first made through or is moderation. IS there a way to contact the program/support of ” Spam Fighters team” for Hotmail/ ? Due to bad design I accidentally clicked up their unsubscribe link in one of their messages and then without a confirmation it dumps my on sorry to see you go your opted out page. No confirmation,no rate program or give reason why. Notta. Coming from Microsoft with massive click confirmations clicks for everything it is very frustrating to say the least.

    The virtual assistant was worse than Bing for results. I gave up after up trying to let it resolve and connect to “a live person” after an hour plus Literally left the window open while searching elsewhere and doing other activity. and its still trying at

    Hope someone here can help. Yes the email address is real, that is the plus of the account, it tends to get “list washed ” for being a fake. Leaving the spammers more determined and blatant who hit it. Giving a better sampling rate.

  8. H. Mertens says:

    Spam fighter link in emails appear to be NOT working; just cycled back into the web/owa Inbox page, without the email in question disappearing (as it use to do, after giving an ambiguous confirmation as marking the email as spam or not spam).

    BTW: Never did like the confirmation email; was never clear if the sampled email as confirmed as SPAM, or in some cases, where it was not, as NOT SPAM – same message non-committal message that could apply to either, without informing whether intended action was acted on.

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