Why doesn’t blocking email senders work?

Most email programs can block email from a specific address. Unfortunately, blocking email from a sender is ineffective when it comes to spam.

How can I block addresses that come repeatedly to my junk email box? It says I am blocking email but it does not work.

In my opinion, blocking email by sender is seriously overrated.

It promises to prevent a sender’s email from reaching you, but if that sender is determined enough, the block is easily bypassed.

And spammers are determined … boy, are they determined! So much so that blocking senders is pretty much useless in the war against spam.

I’ll explain why, and what I’d do instead.

Blocking email and the spam folder

I want to start by clearing something up.

You said that the mail is coming “repeatedly to my junk email box”. That may be what blocking email means in your email program: “when email from this sender arrives, put it in the junk folder”.

That’s what the junk folder (often also called the “spam” folder) is for, and that’s one definition of blocking email.

Different email programs use different techniques and definitions, but if that’s the way your program works, then it’s working as expected.

Misleading email addresses

Stop!Spammers work hard to mislead you. One technique is to make emails look like they’re from someone that they’re not.

Email addresses are typically comprised of two parts: the email address itself, and an optional “display name”. For example, you might see:

From: Leo A. Notenboom <leo@somerandomservice.com>

There you can see both the display name, “Leo A. Notenboom”, and the email address, leo@somerandomservice.com, and it’s pretty obvious which is which.

The display name is optional, but if it’s present, many email programs will display it, and not the actual email address. In that case, your email program might show you something like this:

From: Leo A. Notenboom

Your email program might show you the actual email address if you hover your mouse pointer over the display name, or perhaps click on it.

Spammers, on the other hand, often do this:

From: nancy@reallybigbookstore.com <leo@somerandomservice.com>

Here the display name is “nancy@reallybigbookstore.com”, but the actual email address is “leo@somerandomservice.com”. So in some email programs, you would see this:

From: nancy@reallybigbookstore.com

It looks like email from nancy@reallybigbookstore.com, but it isn’t.

You can block “nancy@reallybigbookstore.com” if you want, but that won’t block this particular email, because that’s not where it actually came from.

Ever-changing email addresses

Because spammers can manipulate the “From:” address so easily, there’s another technique they use that renders individual address blocking completely ineffective.

They simply don’t send “From:” the same address more than once.

You might get the exact same spam over and over, but each time it’ll be “From:” a completely different address. You can block that address if you like, but that won’t impact the next email they send, or the one after that, or the one after that, because they will come from a different address.

Couple that with the tricks spammers use to mislead you as to exactly what email address is really being used, and things get very confusing very fast.

The short answer is that using sender blocking to stop spam is a waste of time and effort.


Don’t block.


Most email programs, and almost all web-based email services, mark emails as spam. This allows the service to learn what is and isn’t spam. While the spam may not get blocked immediately, as you report more and more spam over time, more of it will get blocked: the software will send it to your spam folder instead of your inbox.

Google’s spam filter (as used in Gmail) seems to be particularly effective these days.

If that doesn’t work, I suggest you relax and just use your Delete key. It’s simple, quick, and 100% accurate.

Is blocking good for anything?


Blocking email is good as a start for just about anything that isn’t spam.

For example, if there’s an individual that you specifically want to block, you can block their email address.

But as I mentioned earlier, even then, blocking will be ineffective if they are sufficiently motivated to get through.

All they need to do is get a new email address to send from… and those are trivially easy to get.



  1. Ian

    One approach which takes time, but seems to work is to identify the isp from the headers and complain to them. Several tiresome spam mails sent many times have stopped after I reported their activity to the ISP. Only works with reputable ISPs

  2. thomas smith

    hi , i agree that the block option is not perfect but in hotmail it works for me mostly. I just delete the junkmail folder all at one time. also the sweep option helps a bit

    • rocketride

      My problem with autodeleting the spam folder is that every time I check mine, there’s something in there that shouldn’t be. Thunderbird seems to be particularly bad at learning from what I mark and what I unmark, what I consider spam. So, I’m stuck with actually looking in there and manually deleting every couple of days (or when someone says they sent something and it doesn’t show up in my main box).

      • Mark Jacobs

        Unfortunately, even with the best spam filters, it’s necessary to look at the emails before deleting them. You probably don’t want to lose that one in a thousand legitimate false positive. For example, if you really did have a rich long lost relative who happens to be a Nigerian prince die and leave you millions :) .

  3. Alex Dow

    Check whether the JUNK Directory can be set to Delete IMMEDIATELY or after a given period such as 7 Days with my ISP.

    I have mine set to the “7 Days” Option; but I do go in about three times per day, do a quick check occasionally to see if there are any genuine messages – then Delete them en-bloc, ie a single instruction gets rid of 500 messages etc.

  4. Byron Sevario

    I wish there was a way to destroy the computer that the email was sent from. I hate those Sex spams.

    But knowing that you can’t do that just keep deleting them. That works every time.

  5. Dave

    In Hotmail, email blocking does NOT work! It seemed to for a while, but recently emails I have specifically blocked come right through. Contrary to your article, they have not been change to cleverly get through, but are exactly the same. Is this feature defective?? What do I do? Thanks..

  6. mario

    The problem with the coming back mails in the junk that you already ”sweeped” and ”blocked” is the following :
    you can sweep and you can block mails that you can direct to your Delete mails, or even not to come back ever, is that Hotmail have a capacity of only ‘500’ mail to block under Options/Safe and blocked senders !
    Anything more shows you during sweeping that it is blocked but in fact it is not !!!
    Under Options also, for the rules of sorting messages it has also a limit on the number ‘250’ if i remember and then it stops redirection of mails.
    Nowadays you need at least a good ‘2000’ capacity to limit what you receive and Hotmail is not expanding it.
    Already i mailed Hotmail on that but the answer always : How to sweep and it is a false statement because of the lomit on the volume to sweep.

  7. Najam Bhutta

    Microsoft software engineers write all kinds of programs in the field but how come they can not write a program that can block spammers. I think they do not want to do it purposely. Probably, they have financial interest.

  8. connie

    The problem is that the spammers are also good programmers. They are, by the very nature of what they are doing, always ahead of the anti-spam guys. Same thing with malware writers.

    The bad guys think of a new way to get through the system, and then the system engineers have to first discover the breach, and then write a new block. So the spammers are always ahead of the game because they are creating the game.

    You are absolutely right that they have financial interest. Unfortunately for us the “They” are the spammers. They do it because it works and they can make a lot of money from it.

  9. Mark Jacobs

    In Outlook (in MS Office) the command to mark as spam is called block sender. This should also train the spam filter. MS has a tendency to use confusing terms sometimes :( .

  10. ian minter

    I agree that the process of blocking the sender does not work, but I prefer to create a rule containing the offending “text” within the subject matter / title of the mail and that takes care of all the mails from spammed addresses, as it takes the content of the mail rather than the actual sender.

  11. Beverley

    When gaming in games.com ONLY, my mouse goes jerky after 4 games and I have to restart PC and then it works again. Thank you. Hope you can help?

    PS I enjoy your newsletter very much.

  12. Mike Hamilton

    My ISP provides a service that I believe you can buy for your own use. It works better than any I have even seen, requiring only a glance once a week to free any false positives, which are very rare. it’s Antespam.com, and it typically blocks at least 95% of the spam going to four addresses, numbering more than a hundred, with maybe one mistake a week on one address. My outlook.com (hotmail) acount does exactly what it promises, too. The senders marked go straight to the junk mail folder, where they are easily ignored and easy to delete.

  13. Jack Hewes

    I agree with Ian Minterin his statement about blocking the “offending text” .
    I use Eudora and it has multiple choice’s as what to look for when creating filters for email.
    Eudora allows you to send it to the junk or trash mailbox (Eudora’s term for folders), your choice.

  14. Dan C

    I too had the same problem, rather i still do but what I did was buy a program called mailwasher and I run that program to see the who what and where, without downloading all that crap. I can then look to see if it is junk or not and with a simple click delete the junk from the good mail and it deletes it off my ISP email account and opens up my email program and downloads the good email automatically. This way I don’t even download the junk to my computer and it also keeps track of junk and malware and virus email and marks it for deletion. From what i understand is that it just gets the user name, subject and the first 20 lines if you need to see if it is good or not.

  15. J\Jerry Falk

    Leave you spam in the spam filter for 30 days, then G-mail will delete it. They told me that a spam that sits in the spam filter thirty days is thought by the spammer to be a dead address and they will stop using that address. That’s what I do.

  16. J\Jerry Falk

    I never delete spam, I let it go into g-mails filter and they delete it after 30days. It also shows how many spam are in the filter. Sometimes there 1500 or more, I could care less, and I never check it. The people or companies that I want to email me get through. I’m not concerned with any mail that doesn’t get to me. Just like my cell phone, if I do not recognize the number, I don’t answer it. And snail mail, if I don’t recognize the sender it goes right in my shredder unopened. There are to many junk emails, junk phonecalls and junk letters to waste my time on.

  17. KD

    I use Gmail in addition to AOL mail (which I joined in 1996). In spite of all the negative Internet comments about AOL service, it has done a good job handling SPAM emails to my account. Gmail also does a good filter job.

  18. James B

    In Thunderbird, I’ve had good luck with a filter that marks all email as spam and moves them to the junk folder if the sender is not in my address book. It works well for me because I almost never get email from people I don’t know.

  19. Juan

    Thank you very much, Leo, for sharing your passion and knowledge with all of us! Personally I prefer to delete the spam folder manually, as I don’t receive much spam to create a rule in order to block them. A good idea could be to create a separate email address and use it in all public forums and web sites, and to have another email account that is suitable for private and serious purposes (work, family and close friends, to name a few). Best regards from Paraguay, South America

  20. Chris Banzet

    Being an X_Army vet, I just want to know the IP Addresses location.. Leave the rest to me after that.. 😉 I’ll guarantee a 100% spam blockage after that! It’s getting to the point now where the laws don’t protect consumers at all, and the local municipalities don’t care anymore. It’s funny how governments can DEMAND routes back to our information, but that same “standard” isn’t applied for protection to all… If a person can send something, then a person should have to be registered and accountable.

    We all know that each and every email DOES have a fingerprint. Governments use this information all the time to track sources. In my humble opinion, that SAME information should be kept on file as “record” by the ICAAN group and “PUBLICLY” displayed…

    Sure, a majority of information is sent from spamming services, and since these companies are making “profits” from our painful experience, they should be “publicly” available for reverse pain that we provide them… In my opinion, this would “quickly” bring about “balance” in internet accountability…

    • Mark Jacobs

      Since most, if not all, spammers operate out of country with lax enforcement, I’m not convinced those ideas would help.

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