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Marking spam as spam is an important tool in the war against it, but exactly what happens when you do so is clouded in mystery.

I am on AOL and when I get an email from someone that I do not want to ever hear from again, I report it as spam. What really happens to it? Does AOL know what to do with it if it ever shows up again? Is there any protection for me? Does the person that sent the email know that I put it in the Spam folder?

There's no definitive answer on exactly what happens (for reasons that I'll explain in a moment).

However, there are definitely some general concepts that come in to play when you mark something as spam.

The first distinction is to understand whether you're marking as spam in an email program running on your machine or on a web-based interface.

Marking spam in your email program

By email program, I mean software that runs on your computer and downloads your email from your email service to your computer.

Examples of these kinds of email programs include Outlook, Thunderbird, Windows Live Mail, Windows Mail, and Outlook Express, but there are quite literally dozens of others as well.

When you mark something as spam (or "junk" in some programs), you are telling only that program that the email message is junk. This information typically does not make its way back to your email service provider and does not affect what email will continue to be downloaded in the future. There are exceptions, but they are rare.

"... spam detection is an inexact and ever-changing science."

Identifying spam

Your email program can use the fact that you've marked something as spam in a couple of different ways:

  • It might add the sender's email address to a block list. (This is a separate function in some email programs.) Unfortunately, block lists based on email addresses are typically not effective in the war against spam these days.

  • It might add the IP address of the sender or the sender's email service to a block list. Once again, IP-address-based blocking is also not effective against spam.

  • It might analyze the contents of the message, identify various characteristics of the message, and update a database of information kept by the program that says, "Email that looks like this might be spam, according to the user of this email program." This is the most common and currently the most effective email-program-based, spam-filtering technique.

As effective as it can be, the problem with that last one is that its effects are difficult to predict. You might get an email that is clearly spam to you, mark it as spam, and then later get another that was still not filtered. These types of "learning" filters don't necessarily act immediately, but build up these statistical characteristics of what spam looks like to you over time. It might not be until the second or third (or fourth or tenth) time that you mark a particular type of spam as spam that the filter will finally kick in and automatically identify similar messages as spam in the future.

"Similar" is, after all, a fuzzy concept.

Filtering spam

Great, your email program has successfully identified something as spam – what does it do?

Most email programs do nothing more than move the email to a junk or spam folder.

It sends no notifications back to the sender and no notifications to the email service.

Spam filtering is nothing more then directing flagged email as it's downloaded to your PC into a different folder where you can ignore it.

That's it.

Marking spam on an email service

If you're using your web browser to read your email, you're using an online email service. Your email is stored "in the cloud," not on your PC, and you're simply viewing it via a web-based interface.

Examples of web-based email services include Hotmail, Gmail, Yahoo Mail, and many, many others. Your own ISP or email service may provider may also have a web-based interface to your email in addition to the services that allow you to download it to your PC.

The important thing here is that you're using your web browser to interact with your email stored on your email service's server.

Identifying spam

When you mark something as spam on an online service, you're doing essentially the same thing as you did above with a PC-based email program – you're telling the service, "I think email that looks like this is spam."

The difference, however, is that you're telling the service provider. In fact, you and all of the other users of a particular service are telling the provider what does and does not look like spam.

Exactly how the service provider uses that information is a mystery. For one thing, they don't want spammers to learn the details of the mystery; that would make it possible for spammers to know how to work around it. For another, how service providers use it is constantly changing in response to the ever-changing nature of spam.

There are several approaches that the providers may or may not use:

  • Only things that you mark as spam are used to identify and filter spam for you. This is basically the PC model at the server level – you're not impacted by the spam decisions of other users.

  • Your marking something as spam goes into a single database that's used for everyone. Only things that everyone thinks look like spam are actually filtered. No matter how often you mark something as spam, if everyone else on the service treats it as legitimate, you may never see it filtered.

  • Hybrid: A global sense of what everyone thinks is spam and a local sense of personal preference as to what you think is spam are used when filtering email destined for your inbox.

My sense is that it's mostly the later, hybrid approach, but as I said, it'll vary from provider to provider, and it'll vary over time.

Filtering spam

Much like the email program on your PC, when spam is filtered by an email service, it is typically sent into a junk mail folder in your account. You can then usually safely ignore it or periodically check it for false positives.

And once again, no notice is sent to the sender. The email has, in fact, been delivered; it's just been delivered to your Spam folder.

Some services will take things a step further.

Some services will identify spam at a global level – perhaps based on content or source or something else – and block it from being delivered entirely. You'd never see it in your inbox or in your Spam folder. From your perspective, it's like the email was never sent.

Occasionally in these cases, the service will send back a bounce message to the sender.

Maybe. There's no guarantee.

False positives

Regardless of whether you use PC- or web-based email, spam detection is an inexact and ever-changing science. You'll see email that you consider to be spam – perhaps even obviously spam to you – be delivered into your inbox.

So, you mark it as spam and your email program or service learns a little more about what you consider to be spam.

Occasionally, however, legitimate mail will get marked as spam and be filtered. This is referred to as a "false positive."

For anything that's been filtered and placed into a spam folder, you should have the ability to say, "This is NOT spam".

This is perhaps even more important than identifying spam.

Once again, the program or service takes this indication from you and learns from you that email like this should not be considered spam.

That's an important step to take. Every so often, spend a few minutes in your Spam folder looking for things that were filtered and should not have been. Mark those as "not spam" to reduce the chance of similar mail in the future also being filtered.

Article C5330 - May 12, 2012 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

May 15, 2012 7:50 AM

>I am on AOL and when I get an email from
>someone that I do not want to ever hear from
>again, I report it as spam.

Spam reports should be limited to real spam, not people you just do not want to hear from again. If you subscribed to a newsletter, for example, unsubscribe don't report it as spam.

Stephen Clark
May 15, 2012 11:58 AM

Hi Leo
Might it not be worth mentioning the activities of internet security programs in this context? I use Kaspersky and it has certainly taken a view on email spam in the past and I have had to edit the reports on occasions to stop it marking stuff that is genuine.

May 15, 2012 12:50 PM

AOL and blacklisted my web address some time ago. It only affected their subscribers, and eventually an IT savvy pal got the blacklisting lifted. I don't know if my e-mail address was spoofed, or why the blacklisting was imposed - AOL won't say.

Then another ISP blacklisted my web address, but that has been lifted as well.

Jason Ciastko
May 15, 2012 12:57 PM

A good resource for people to learn about SPAM and how to prevent it is the excellent website by Randy Cassingham that can be found at Between this and Ask Leo, you can't find better information on the internet...

May 15, 2012 1:09 PM

In reply to Ronny's statement - Be very careful when unsubscribing. In the past I have unsubscribed to some emails - and all that does is confirm they have a live one, and start selling your email address to other sources (I sometimes use different upper/lower case combos when I register - so I know what sites do it - and it can happen with quality sites). If it is unsolicited, I will mark it as spam. I will only unsubscribe to sites that I have subscribed to in the first place that I believe are not going to sell my address.

Alex Dow
May 15, 2012 11:20 PM

With my Mail Provider/ISP, I can insert e-mail addresses that are either Accept or Reject.

Originally, my impression was that the lists could only accomodate specific addresses on the lines of-

Fine if only one person; but a nuisance if several were involved, gradually changing as individuals left and joined that company, so tedious to update.

Recently, I found that the lists could accomodate all of the company employees by using the generic part of the address, ie-

Proven to be very usefull.

May 16, 2012 4:01 PM

I use Thunderbird. I created a filter that puts all email from people who are not in my address book into the Junk mail folder.

I find that more effective than marking something as spam, as the spam filter might take a while to learn that it is spam. Periodically, I'll scan through the Junk mail to see if there is something legitimate.

August 3, 2012 6:36 AM

A lot of spam these days has my own address spoofed into the From: field.
Is there (or can there be) detrimental effects of marking "yourself" as spam? I know a lot of programs / interfaces will not let you blacklist yourself, but this is different.

Mark J
August 3, 2012 10:10 AM

It's not a good idea to mark an email return addressed from yourself, especially if you are doing this on a web mail interface. It could cause that provider to flag your address as spam.

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