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What’s the Difference Between Spam and Junk Mail?

Question: I use Thunderbird to download my email. Most of my email addresses are “” Each of those addresses have both a “junk” and a “spam” folder. Virtually everything that shows up in the junk folder is spam and everything that’s in the spam folder is junk. What’s the difference between the two folders? My more important question: for quite awhile I have been marking all my many emails in my spam folder as junk, moving them to the junk folder, and then deleting them. By doing so is Thunderbird and/or AOL “learning” anything — or am I just wasting my time?

This actually represents a couple of very common points of confusion. One is very easy to clear up; the other, not so much.

First, the easy: the terms junk and spam are synonymous. Some email programs or services call it spam, some call it junk mail, but it’s the same thing in either case. What you’re seeing in Thunderbird is what happens when those worlds collide.

The confusion about training the spam or junk filters, however, is both important to understand and somewhat more complex. While I’ll use your AOL account as an example, this applies to all email services and all desktop email programs1 that have spam filters.

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Spam versus junk

So, if it’s one or the other, why do you have both “spam” and “junk” folders in Thunderbird?

Thunderbird uses the term “junk”, and its junk mail filter moves what it considers to be junk into a folder called “junk”.

AOL uses the term “spam”, and its spam filter moves what it considers to be spam into a folder called “spam”.

You probably have Thunderbird configured to access your AOL account using the IMAP protocol. (See What is IMAP? And how can it help me manage my email? if you’re uncertain what that is.) IMAP causes the folders on your AOL account to be downloaded into your email program…

…including the “spam” folder. So you end up with both:

  • Thunderbird’s “junk” folder
  • AOL’s “spam” folder

How local and remote spam folders interrelate

SpamWhen email sent to you is received by AOL, it is analyzed by AOL’s spam filter, and email considered spam is moved to the spam folder.

When downloading email into Thunderbird, that email is analyzed by Thunderbird’s junk mail filter, and email that is considered junk is moved to the junk folder.

Knowing that “junk” and “spam” are two words for the same thing, you can now see you have two completely separate spam filters working for you:

  • AOL’s, on the AOL server, when your email arrives and before you download your email
  • Thunderbird’s, on your PC, when you download email

In theory, Thunderbird would mark as spam/junk anything that AOL might have missed.

It’s kind of an accidental belt-and-suspenders kind of situation.

What trains who?

The real confusion happens when you mark something as spam or junk in order to train the filters. Which filter are you training?

When you mark something “as junk” in Thunderbird, you are only training Thunderbird’s junk filter. The AOL spam filter never hears about it, and thus has no way to know.

In order to train the AOL spam filter, I believe you actually have to log in to AOL’s web mail and mark things as spam there. That will move the message to AOL’s spam folder, and should even cause it to appear in the spam folder when you view it in Thunderbird. But in this case, Thunderbird’s junk filter will not have been trained, because it has no way to know what you did online at AOL. That the mail appears in the “spam” folder means nothing, since to Thunderbird that word has no special meaning; what AOL calls “spam”, Thunderbird calls “junk”.

I don’t believe simply moving messages between the junk and spam folders trains anything.2 I think it’s the “mark as” action in either location that actually does the training, but only for the location in which you perform the action.

If you want to train both AOL (the service) and Thunderbird (the desktop email program), you have to mark spam or junk in both places.

Other services and programs

This confusion happens all the time, and applies to all email services that filter spam online, as well as all desktop email programs that filter for spam.

That you happened to have both a “junk” and a “spam” folder just made it more obvious.

When your email service and your email program agree, and both use the term “spam”, for example, you may have two separate spam folders – one managed by the email service’s on-line spam filter, and the other managed by your desktop email program.

Or you may have a single spam folder into which both place the messages they identify as spam.

But one thing remains constant: when you “mark as spam” (or junk), that trains only the online service (if you’re doing it in a web interface) or your desktop email program (if you’re doing it on your PC). I know of no way to tell them both at the same time.

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Footnotes & references

1: I’m using “desktop email program” to refer to any email program running on your computer or device, such as Thunderbird, Microsoft Office Outlook, the Windows “Mail” program … or the mail program installed on your mobile device, as opposed to accessing your email online via a web interface, or a service-specific mobile application like Gmail.

2: I could be wrong, but it almost certainly varies depending on the email provider and email program you happen to be using. It’s not something you can count on, in any event.

12 comments on “What’s the Difference Between Spam and Junk Mail?”

  1. Yahoo works the same, except they call it Bulk. I just told Thunderbird that the spam filter was the Bulk folder. Then I deleted the default Spam filter and now I only have one folder for spam.

  2. What confuses me is there is a particular email I get from an email list I never signed up for. Following Leo’s advise, I won’t unsubscribe but mark it as spam. However Thumderbird keeps taking the spam flag off the email every time I mark it as spam (not each week’s version, but the same email). I’ll click Mark as Spam 10 times in a row and 10 times in a row Thunderbird will remove the flag. Then occasionally, I find a newsletter I want has been marked by Thunderbird as spam. I unmark it, yet Thurnderbird keeps marking it as spam. We have a continual fight until I finally give up figuring I can’t beat the computer. Why?

    • I have the same issue with Thunderbird: a newsletter which I want to receive always ends up in the spam folder. No matter how many times I mark it as not spam, it gets reverted to marked as spam by Thunderbird. The email address of the sender is whitelisted, but its spam filter seems to overrule this. Once I even deleted Thunderbird’s entire spam databse and retrained it. This did not work either: after a while was the newsletter again marked as spam.

  3. Thunderbird insists on marking your newsletters as junk. Every time I get a newsletter I mark it as ‘Not Junk’ and click on ‘Ignore warnings about this message’. In addition, I have your address in my address book, but it is still happening. How long does it take Thunderbird to learn?

  4. Leo’s Newsletter is marked as junk by Thunderbird on my PC as well.
    It also marks as junk two other newsletters I get from US sites.
    UK newsletters get through AOK

    I’ve been marking the US newsletters as not junk for at least 3 years, so it appears to take time – ah well curiouser & curioser

    • Strangely enough, Bob Rankin’s newsletters get through with no trouble. What’s Leo done to upset Mozilla? :-) Just joking.

  5. Thanks very much for your informative article. I’ve always wondered why I had duplicate “spam” and “junk” folders in some of my Thunderbird email accounts, and not others. Now I know!

  6. I have instructed my Thunderbird spam filter to send spam to the Spam folder for the account instead of the Thunderbird Junk folder. That way all my spam is in one folder and the TBird Junk folder is always empty.

    One thing I used to do is with any mail sent to the spam folder, I’d mark it as junk in Thunderbird so Thunderbird gets the extra training. But I think that was overkill.

  7. Come on LEO. Saying “IMAP Protocol” is saying “Internet Message Access Protocol Protocol” :-)
    (Your personal grammar Nazi)


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