Own tricks to stay free of spam

Erik's notes on

Erik Thau-Knudsen

Nobody likes spam or junk mail, yet some of us want to be accessible to other people through the Internet. This page deals with various ways to trick the spammers, tricks that go beyond what spam filters can do. My treatment of spam filters will, thus, not be in-depth. Also, server side e-mail scripts will not be treated, as these require expert knowledge.

  1. Personal behavior
    1. Keep it all secret
    2. Give it only to people you trust
    3. Keep your e-mail address changing
    4. Use aliases. Set up and delete when needed
  2. Spam filters
    1. Remote side spam filters
    2. Own server-side spam filters
    3. Client side spam filters
  3. E-mail addresses on web pages
    1. The wrong way
    2. Plain text
    3. Spelling it out
    4. Tables
    5. ASCII coding
    6. JavaScripting
    7. Imaging
    8. Background imaging

Personal behavior

There is really much to be achieved if you behave with the necessary caution. You should pay more or less the same caution as when giving your snail mail address away to any other postal order company.

Keep it all secret

Don't hand over your e-mail address to anybody. Keep it in your locker, swallow the key, never open your mailbox.

Pros

Cons

Give it only to people you trust

Deliver your e-mail address in a handwritten form or dictate it by phone. Make sure it will only stay on their personal address books. Make them promise that they never show it to anybody.

Pros

Cons

Keep your e-mail address changing

Set up an address on your mail server of the kind my-name_2005@my-domain.dk. In 2006, change it to my-name_2006@my-domain.dk.

Pros

Cons

Use aliases. Set up and delete when needed

Some internet providers offer aliasing, i.e., a number (sometimes unlimited) of different names for the same recipient. All e-mail for the aliases will be directed to the same mailbox. I met a guy in 2004, who does this. For his participation on the Danish web portal Jubii he has the type jubii@my-domain.dk; in his Macintosh user group he uses macuser@my-domain.dk, whereas while at work he uses the type work@my-domain.dk.

Pros

Cons

Spam filters

As I told in the beginning, spam filters is not my specialty. The below chapter is an outline only.

You may set up spam filters. The ones existing to-day can be divided into roughly three types, at least, all depending on which fase of the transmission we are dealing with:

  1. Remote side spam filters
  2. Own server side spam filters
  3. Client side spam filters

Remote side spam filters

This type is a filter that a server may have set up to prevent that his server, sometimes even a SMTP server will be used by a junk mail emitter. Some of the on-line e-mail services, such as Eudoramail, will prevent you from creating maillists with more than 20 addresses. This is good, because often spammers use well-known domain names as their addresses, such as yahoo.com, hotmail.com etc. Sometimes this happens even within the mail program which may have an upper limit of names in an address list.

FYI: Around 2001, I got an offer (by junk mail, can you believe it?) of a CD-ROM with 2 million valid e-mail addresses. Not doubt how this should be used.

Own server-side spam filters

Many e-mail providers offer junk mail filters. These filters filter off spam mail by analysing all incoming mail by specific parameters, such as domain names renowned for hosting notorious spammers, or mismatching sender addresses.

Client side spam filters

Many e-mail programs offer junk mail filters. The free Gecko based programs (Mozilla, Netscape 6+, Thunderbird) and Apple's Mail have intelligent spam filters, by which you teach the filter what is spam and what is not. It takes some time, but once they're up and going, they are quite satisfactory.

E-mail addresses on web pages

If you write your own web pages, you are more in control with how to do things. More control does not necessarily keep you spam free. This section deals with what you can do with HTML to prevent robots (automatic programs updating the contents from HTML documents) from interpreting e-mail addresses.

The wrong way

HTML code Representation in browser
<span><a href="mailto:my-name@my-domain.dk">My name</a></span> My name

Pros

Cons

Plain text

HTML code Representation in browser
<span>my-name@my-domain.dk</span> my-name@my-domain.dk

Pros

Cons

Spelling it out

HTML code Representation in browser
<span>my-name at my-domain dot dk</span> my-name at my-domain dot dk

Pros

Cons

Tables

HTML code Representation in browser
<span><table><tr><td>my-name</td> <td>@</td><td>my-domain.dk</td></tr></table></span>
my-name @ my-domain.dk

Pros

Cons

ASCII coding

HTML code What the browser reads What the browser displays
<span><a href="
&#109;&#97;&#105;&#108;&#116;
&#111;&#58;&#109;&#121;&#45;
&#110;&#97;&#109;&#101;&#64;
&#109;&#121;&#45;&#100;
&#111;&#109;&#97;&#105;&#110;
&#46;
&#100;&#107;">My name</a></span>
<span><a href="mailto:
my-name@
my-domain.dk">
My name</span>
My name

Pros

Cons

The ASCII model can be twisted ad infinitum. You might add enough characters to display

<span><a href="mailto:'My name' <my-name@my-domain.dk>">My Name</a></span>

I expect that this will really confuse the robot. It will also be more convenient to the user, whose Recipient field will be properly filled in.

Link

Asciitable.com

JavaScripting

HTML code What the browser displays
<span>
<script type=text/javascript>
//<![CDATA[
document.write ('<a href="');
document.write ('mailto:');
document.write ('my-name@');
document.write ('my-domain.dk');
document.write ('" title="Click to send me an e-mail using your own
e-mail program.">');
document.write ('my-name');
document.write ('@my-domain.dk</a> ');
//]]>
</script>
</span>

Pros

Cons

Frankly, this model is my favourite.

Imaging

Three varieties
HTML code What the browser displays
1. @ as an image  
<span>E-mail: My-name<img src="images/at.png" alt="at" />my-domain.dk</span> E-mail : my-name atmy-domain.dk
2. my-name@my.domain.dk as an image  
<span>E-mail: <img src="images/my-name-at-my-domain.png" alt="My name at my domain" /></span> E-mail :
3. E-mail: my-name@my.domain.dk as an image  
<span><img src="images/my_e-mail.png" alt="My e-mail" /> </span> My e-mail

Explanation

All three varieties are built on the principle that instead of text, the junk mail www robots will get images and thus not be able to decode them. After all, they are just programs, not human eyes.

Using images to cover e-mail addresses is an approach often used on the World Wide Web.

Pros

Cons

Background imaging

HTML code What the browser displays
<span style="height: 13px; width: 156px; background-image: images/my-name-at-my-domain.png; background-position: top left; background-repeat: no-repeat;">
<span style="visibility: hidden; ">See my e-mail with an image enabled browser!</span>
</span>
See my e-mail with an image enabled browser!

Explanation

This trick is inspired from Zen Garden, a group of web designers that aim to show the supremacy of the Cascading Style Sheets technology over styling with HTML codes only. The principle behind is a bit like the previous trick — to use an image to replace text. Here, though, I made it a background image. To make sure you won't see multiple images, you will have to add the information background-repeat: no-repeat;, whereas the CSS property background-position: top left; is not that important, since it is the default setting of most desktop browsers.

To aid people with non-image browsers such as Lynx or aids for visually impaired, I added a dummy text. In fact the trick won't work unless you add some text to the second <span> tag. It will not be seen by users with regular browsers because I added the the property visibility: hidden;.

Using <div> tags instead of <span> tags is better, because the former are more obedient to the CSS height and width properties than are <span> tags.

I have not used this trick, but feel free to do so.

Pros

Cons

 

Erik Thau-Knudsen

2007-05-28