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Blocking senders is an ineffective way to deal with spam, but Thunderbird includes the ability, along with an adaptive junk mail filter.

I have used Thunderbird, but my one complaint is that it takes a technician like yourself to block unwanted emails. With Outlook Express, it's very simple. Can you advise me how to do this easily with Thunderbird?

It depends on what you mean by "blocking unwanted emails."

If you mean spam, Thunderbird has a built-in spam filter, just like Outlook Express had. While no spam filter is perfect, marking something as spam is pretty easy.

If you mean that you want to block specific email addresses from showing up in your inbox, that too is very similar to Outlook Express's approach. Just be aware that blocking senders by email address is not an effective way to stop spam, no matter what email program you use.

Thunderbird's Junk Mail filter

Like some email programs, Thunderbird refers to spam as "junk mail" and includes a junk mail filter that can be trained over time - the more email you marks as spam, the better Thunderbird gets at identifying spam automatically.

If you use multiple email accounts, then unlike many programs, Thunderbird allows you to control junk mail differently for each account.

In Thunderbird, click on Tools, Account Settings..., and then Junk Settings within the email account you want to configure.

Junk Settings in Thunderbird's Account dialog

In the example above, I'm looking at the Junk Settings for my first configured email account (if you have only one email account, it'll be the first as well Smile). "Enable" is checked to turn on the adaptive filter. I've also specified that if the sender of an email is in my Personal Address Book, email from that person should never be marked as junk.

Finally, I've indicated that junk mail should be automatically moved to a Junk mail folder.

Training the Junk Mail Filter

Once you've got it enabled, you can start telling Thunderbird what is and is not junk.

In the message list, there's a small "flame" icon (enlarged here):

Thunderbird spam flame icon

Looking in list view, you'll see one of the column headers is that flame:

Spam column in Thunderbird list view

If the message has a flame icon and it's not really spam, click on the icon to unset it. If the message is clearly spam (as the examples above all are), then if the icon is not set, click that message in that column to set it. Thunderbird will now treat that message as spam and use it to 'learn' what you think is spam.

Similarly, if you're looking at a full message, there's a Junk button available to tell Thunderbird that what you're looking at is spam:

Thunderbird junk button

Filtering specific senders

If there's a specific email address from which you never want to see email, just like Outlook Express, you can use message filters to dispose of the messages as soon as they arrive. There is no way to prevent the messages from being sent to you - again, regardless of what email program you use - but you can make them disappear as soon as they show up.

On Thunderbird's Tools menu, click on Message Filters...:

Thunderbird's Message Filters dialog

Again, Thunderbird allows you to maintain a different set of filters for every account you use, so start by selecting the account in "Filters for:". Then click on New...:

Thunderbird delete filter

In the example shown above, I've defined a filter:

  • It's named "Delete mail from Fred."

  • It looks for "From" containing Fred's email address (

  • When it finds mail that matches that condition, it deletes the mail immediately.

With that rule, I'll never see email from Fred again.

Naturally, you'd add whatever conditions and email addresses you would want to block.

Click OK.

Thunderbird filter list

We now have a blocking filter.

Why is there no Block Sender...?

Block Sender... in Outlook Express is really just a shortcut that does the equivalent of creating the filter we created above. (Outlook Express kept this as a separate list - no actual filter was created - but it was essentially the same thing.)

Outlook Express' Block Sender

The problem is that Block Sender... doesn't work.

"The 'From:' line in spam is now completely meaningless ..."

More correctly, Block Sender... doesn't do what most people think it does.

Block Sender... doesn't stop spam. It doesn't even make a dent in it.

Spammers caught wind of Block Sender... years ago, and they render it completely ineffective simply by sending their messages from hundreds of thousands of randomly chosen spoofed email addresses. The "From:" line in spam is now completely meaningless, and it's completely pointless to try and block the supposed sender of spam.

Building a block senders list to stop spam only slows down your email program as it has to check every email that comes in against the list.

And it doesn't work.

It will not block, or even slow down, spam. The only thing it will slow down is your email program.

Use the spam or junk email filters to deal with spam.

Create sender-blocking filters when you have an actual, specific email address that you know is repeatedly sending you something you never want to see.

Article C5220 - April 18, 2012 « »

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?

April 20, 2012 3:01 PM

I can recommend 'Mail Washer' as a very effective
way of scanning, blocking and deleting unwanted mail and will work with most if not all email clients. Most of which leave a lot to be desired when it comes to preventing spam.
Yours ...

April 23, 2012 1:29 PM

You can also use the same filtering mechanism to create a "white list" (I call mine People I Know) and if the person sending the email isn't listed, I won't see it unless I select "All". I do select "All" periodically just clean out the junk and make sure I haven't missed something of value from an unlisted email address. But for day-to-day use, white-listing is an excellent solution.
PS: Make sure that "is in my address book" is included in the list. Saves a lot of aggravation.

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