Yesterday’s Thoughts

June 17, 2005

Thunderbird and Images

If you use Thunderbird to read your e-mail, adding a sender to your Address book will cause any remote images in their messages to be displayed automatically.

That’s all you need to know really. If you want to know why Thunderbird blocks images in the first place read on.

I use Thunderbird as my mail client. For years, I used Eudora which was a very nice client.

Thunderbird is not as mature as Eudora and I would probably still be using Eudora if they hadn’t released updates that didn’t work with Exchange. This left unable to access my mail. Eudora (the company) compounded the problem by having a completely moronic technical support/issue tracking system. Software breaks sometimes. Users can accept this, but if the problem is compounded by having a bug tracking and technical support process that is broken, users are going to walk away, not come back, and tell their friends.

In Eudora’s case they had me fill in an extensive e-mail message which included details about my operating system, version of Eudora, other running software, etc., plus what I was doing when the error appeared. Then, Eudora took a couple of minutes automatically adding the very same details about my operating system, version of Eudora, other running software, etc. That was moderately annoying, but then once the e-mail was sent, I received an immediate response saying that they didn’t accept bug reports or technical support requests by e-mail.

Eudora had released a new version of their software, and hadn’t replaced the text describing the tedious and obsolete bug reporting system.

I found an older version of Eudora and uninstalled the new version, but I was not a happy customer. I was attracted to Thunderbird because it was open source and because they implemented Bayesian spam filtering. If an open source client stops being able to read my mail, I can always fix it myself, and even though I had some pretty good spam filtering on my own, I thought that there could be a better way.

Once other nice feature that Thunderbird had was a high level of built-in privacy protection. One aspect of this protection is that it refuses to open remote images in messages unless you expressly tell it to. Senders can use either an image url pointing to a remote site or an actual image file into an e-mail. One advantage of the remote image url is that if you don’t open up the mail, then the sender hasn’t used their bandwidth to send it to you. I haven’t looked systematically, but my guess is that less than 1/3 of my mail includes the images in the mail. The rest call out to a remote server.

The privacy concern is that the image url can be customized for you and might tell the sender things about you that you don’t want them to know. The sender can know that you opened that piece of mail, when you opened the mail, and how often you opened the mail. If you click on any of the links in the mail, that can also be tracked. All this data is correlated with all of the other information the sender had before they sent you the mail.

How this works Instead of a url like your e-mail will contain a personalized url like
The eMNeTphSv4Q-J9PqeKP is sufficient for the sender to identify both you and the specific message that they sent to you. There are a number of purposes for tracking this information and you can feel different ways about them.

  • Senders want to ensure that you are receiving their mail.
  • Senders want to know that you are opening their mail.
  • Senders want to learn how you are responding to their mail

Senders don’t want to send mail to people who don’t receive or don’t open the e-mail. This can happen because the e-mail is being blocked as spam, because the e-mail is going to users who have closed their accounts, or because the e-mail isn’t very interesting to the people to whom it is addressed.

If you send personalized e-mails to 1 million people every month some reasonably constant percentage of people will open them month after month. If your data collection and reporting is up to snuff you can break those percentages down by the recipient’s ISP. If the percentage of Earthlink users who read the mail goes way down, you can be reasonably confident that Earthlink has decided that you are sending spam. Since the cost of these mails is reasonably high, you will want to figure out why this is, and take appropriate measures.

Detecting closed accounts, uninterested consumers, or consumers who are inadvertently blocking your mail as spam is done the same way. As a sender, perhaps you will want to remove this user from your mailing list, or send them a special message to entice them back into an active relationship with you and convince them to put you on their spam white list.

Determining interest is more complicated. Marketers will track the opens of a piece of mail and any follow on activity. If they are mailing large numbers of e-mails they will sent test messages with different subject lines and/or contents to determine the effectiveness of a given approach. This ability to track the responses of large numbers of consumers directly is a dream situation for marketers.

Many people object to the detailed marketing information being collected on them. Personally, I am not that bothered by this data collection. I just don’t care if Safeway knows that I mostly buy food from the area around the edges of the store, but that I sometimes buy diapers.

If you do object to becoming a marketing statistic, you should not click on any link in an e-mail from a business, as it is likely to be tagged in the same way as the image urls. Do not use any affinity or club card or credit card. Marketing data is collected from all of these.

To get an idea of the value of this data to marketers, measure how much you save when you use your club card at the grocery. As a first approximation, that is the value that the retailer is getting from your data. I routinely save over $5 on a $100 shopping cart.

Since I don’t care about that aspect of my privacy, why do I care about the privacy features of Thunderbird? Simply, they are a deterrent to spam. Spammers use the same methods as legitimate marketers to determine if anyone is home at my e-mail address. I presume that they collect this data and use it to qualify their e-mail lists and add value to that list.

“I have 100,000 e-mail addresses where I know that the user has opened an e-mail in the last 60 days. Let’s start the bidding at $25,000.” I’m making up the auction scenario and the amounts, but I bet it’s not far from the truth.

Thunderbird has a feature to block loading of remote images. With the feature turned on neither spammers, nor legitimate marketers whom I choose to hide from, will know that I have read their messages. When the images are blocked, a bar appears at the top of the message explaining what has happened and button appears in the upper right corner labeled “Show Images.” The button does what you expect and is useful for those cases where the images are interesting to see.

Once you click the button, the images in that mail will appear every time you read that message. This is contrast to gmail, which has the same feature, but forgets so you have to click “show images” every time that you read the e-mail. (Correction: gmail now presents you with a link, “Always display images from”)

Eventually this becomes a pain for senders where you always want to see the images. Until I went to all RSS for my news I received a daily summary of the days events from the New York Times. They were very nice mails. They were laid out to suggest a newspaper, with the bonus that I could select which sections I wanted to see and how many articles in each section. Like a newspaper, there were photos and other images. The trouble was that every day I had to click on “Show Images.”

Yesterday I learned a trick. Right under the check box for blocking remote images, there is a second check box for showing images when sender is in your address book. This doesn’t sound like much, but it is. Once I have added the sender to my address book, two clicks, I can read their future messages without taking my hands off the keyboard and onto the mouse. This is a good feature.

Sept. 18, 2005 – Who wrote this? I have just corrected at least a dozen typos and a couple of places where the language was unclear. Interestingly all of the typos were in the first five or six paragraphs. Either I skipped proofing those ‘graphs, or worse, my eyes just became accustomed to typos and unclear language and I didn’t see any of the typos in the later paragraphs.

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