Home |

Programming Resources |

Anti-Spam |

* The Anti-Spam Home Page The Old Anti-Spam Home Page (archived)

Share This Page

The Old Anti-Spam Home Page (archived)

This is the original anti-spam home page content, preserved for historical purposes.
Click here to go to the current article.

The spam problem is not going away, it's getting worse!
Learn how to stop junk e-mail.

— P. Lutus -- Message Page --

Tired of wading through all that junk mail? Learn how to stop the spammers — here are instructions to automatically filter your e-mail, defend your site from exploitation by the spammers, and get involved!

Use these links to choose the section you are interested in: General discussion Definition of spam Rules of the spam game What to do if you are on a site that permits spam How to alert a site that they are hosting a spammer How to identify a Spammer Spam do's and don'ts Write your congressional representatives How to report fraudulent e-mail E-mail filtering techniques How to edit sendmail.cf How to filter e-mail addresses and sites How to stop e-mail forwarding on your site How to test the changes in sendmail The spammer master lists Credits Other anti-spam resources

• According to some estimates, there are 50 million Americans with Internet accounts.
  
• Nearly all accounts have e-mail service.
  
• It costs virtually nothing to send an e-mail.
  
• There is no meaningful regulation of e-mail.
  

• Use a friend's e-mail account to write the destination site and ask whether your host site has been blacklisted, and the reason.
  
• If your site has been blacklisted because of spam problems, write your own site's support address (usually support@yoursite.com or webmaster@yoursite.com ) and demand that all spammers be thrown off the site.
  
• If your service does not coöperate, change services . Canceling an account is one of the most powerful signals you can send — a loss of revenue.
  

• If you are writing to a legitimate site, they will usually have a special address ( abuse@sitename.com ) set up to deal with the problem. They may thank you for writing and ask for more information (such as the e-mail header, which shows the actual path the e-mail took through the Internet).
  
• If you are writing to a spam-friendly site, chances are they will not write back, or they will reply with a justification of their practices, or (in some cases) they will simply place you address in their master list of victims (this happened to me).
  

• The primary rule: Never make lists of e-mail addresses, and if you do, do not e-mail the list. This is a common practice, especially among the relatively inexperienced.
  It happens like this — Joe Beginner receives an interesting article and he immediately wants to mail it to all his friends — but he does it by including all the addresses in a single posting. The problem? Each recipient gets a copy of all the addresses. Then one of Joe's friends forwards it to all his friends the same way. The address list becomes very large, and finally it falls into the hands of someone in the spam trade.
  Instead, Joe Beginner should mail a separate copy to each of his friends. The point is there should never be more than one address on an e-mail.

• Never respond to a spam e-mail. For a spammer, one "hit" among thousands of mailings is enough to justify the practice. Instead, if you want a product that is advertised in a spam e-mail, go to a Web site that also carries the product, inquire there, and tell them you do not approve of spam methods and will not patronize a company that uses spammers.

• Never respond to the spam e-mail's instructions to reply with the word "remove." This is just a trick to get you to react to the e-mail -- it alerts the sender that a human is at your address, which greatly increases its value. If you reply, your address is placed on more lists and you receive more spam.

• Never sign up with sites that promise to remove your name from spam lists. These sites are of two kinds: (1) sincere, and (2) spam address collectors. The first kind of site is ignored (or exploited) by the spammers, the second is owned by them -- in both cases your address is recorded and valued more highly because you have just identified it as read by a human.

• Never mail-bomb spam sites or engage in hacking to stop spammers. This only increases the amount of wasted Internet traffic, creates sympathy for spammers, and makes the Internet even less reliable than it already is.

• Take meaningful action to stop spammers. Filter their messages or their sites using the methods described below, write their host sites (without revealing your real e-mail address!) and any sites that are used as relays, write your congressional representatives.

1. Write your congressional representative -- click here.
   
2. Write your state's senators -- click here.
   
3. Write the Federal Trade Commission, demand action against spammers -- click here.
   

• FTC Spam Report e-mail address (uce@ftc.gov)
• The Federal Trade Commission Home Page
• The National Fraud Information Center
• A list of State Attorneys General + Agency List

1. Locate sendmail.cf, the sendmail configuration file.
2. Copy the original version to a safe location.
3. Make the changes described below.
4. Create /etc/spammers.txt, a list of e-mail addresses to be excluded from your server.
5. Create /etc/spamdomains.txt, a list of host and domain sites to be excluded from your server.
6. Create /etc/relaydomains.txt, a list of host and domain sites you want to permit relaying through your site (all others will be blocked). This file should be created, even if it has no entries.
7. Put the new version of sendmail.cf in place.
8. Test your mail service to be sure that you have not made an error that might disable e-mail on your site.

#############
#  Options  #
#############
Oa1			# Wait (in minutes) for alias file rebuild
OA/etc/aliases		# location of alias file
OC10			# Checkpoint queue runs every N deliveries
OF0600			# Temporary file mode
Og100			# Default GID
OH/etc/sendmail.hf      # SMTP help file
OI			# Insist that the name server be running
Ok5			# Open connection cache size
Om			# Expand aliases to include sender
On			# Verify RHS in newaliases
OQ/usr/spool/mqueue	# Queue directory
OS/etc/sendmail.st	# Stat file
OT3d			# Queue timeout and warning time
Ou126			# Default UID
Ot			# Use TZ environment variable
                

#################################
#  Ruleset 0 - Resolve address  #
#################################
S0
R<@>			$#local$:<>		Null address is local
                

1. Insert the following section into sendmail.cf at the point specified in How to edit sendmail.cf . This section provides the code for both the address method and the host method described in the next section.

   ##################################################################### # Ruleset check_mail - Stop Spammers (see http://www.vix.com/spam/) # ##################################################################### # spam site list files F{SpamDomains} /etc/spamdomains.txt F{Spammers} /etc/spammers.txt Scheck_mail R<$={Spammers}> $#error $@ 4.7.1 $: "471 We don't accept junk mail" R$={Spammers} $#error $@ 4.7.1 $: "471 We don't accept junk mail" R$* $: $>3 $1 R$*<@$*$={SpamDomains}.>$* $#error $@ 4.7.1 $: "471 We don't accept junk mail from your domain" R$*<@$*$={SpamDomains}>$* $#error $@ 4.7.1 $: "471 We don't accept junk mail from your domain" R$* $@ ok R$* $#error $@ 4.1.8 $: "418 can't resolve your name, check your DNS"

   To capture this code, simply drag your mouse across it and place it in your text editor. If you cannot do this, click here.

2. Create a text file named /etc/spammers.txt (see The spammer master lists for a current list). Put one or more e-mail addresses in the file, each on a separate line.
   Example:
   company1@spamsite.com
   company2@spamsite.com
   This method only filters particular addresses — a determined spammer will not be stopped by this approach. It is too easy to simply create another e-mail address.

3. Create a text file named /etc/spamdomains.txt (see The spammer master lists for a current list). Put one or more host and domain names in this file, each on a separate line.
   Example:
   spammer.spamsite1.com
   spamsite2.com
   The first example above stops all e-mail from the host site "spammer.spamsite1.com." The second example stops all e-mail from the entire domain "spamsite2.com." The check_mail code accepts both kind of entries, depending on your wishes — you may want to stop a particular host, or all e-mail from an entire spammer-friendly domain.
   Stopping all e-mail from a host or domain is more powerful than the e-mail address method — it eliminates e-mail from an entire site, but at the risk of blocking legitimate e-mail. If you receive a complaint from a legitimate user of that site that they cannot e-mail you, just explain that their site permits spamming and ask them to write their site's administrators to correct the problem at the source.

1. Insert the following section into sendmail.cf at the end of the file as described in How to edit sendmail.cf . This section provides code to verify that e-mails are either beginning or ending their journey at your site, and blocks all others.

   ############################################################## # Ruleset check_rcpt - Shutdown relaying through this server # ############################################################## # dequoting map - Needed for SPAM hack below Kdequote dequote # permitted relay sites file F{RelayOK} -o /etc/relaydomains.txt Scheck_rcpt # anything terminating locally is ok R<$+ @ $=w > $@ OK R<$+ @ $* $={RelayOK} > $@ OK # anything originating locally is ok R$* $: $(dequote "" $&{client_name} $) R$=w $@ OK R$* $={RelayOK} $@ OK R$@ $@ OK # anything else is bogus R$* $#error $: "550 Relaying Denied"

   To capture this code, simply drag your mouse across it and place it in your text editor. If you cannot do this, click here.
   Precautions about blocking forwarding:
   • If you want to permit some sites to forward e-mail by way of your site, you must add their host or domain names to a text file named /etc/relaydomains.txt. Create this file if necessary.
   • This code segment, like the previous one, accepts both host (host.sitename.com) and domain (sitename.com) names.
   • With some e-mail clients, this code segment may prevent you from sending mail to other sites. If it does, use this procedure:
     • If you are accessing your Web server from a separate site, add the host or domain name of that site to /etc/relaydomains.txt and test again.
     • If this test fails, simply remove this code segment from your sendmail.cf file.

2. Don't forget to create a file named /etc/relaydomains.txt, even if it is empty. Enter the names of any sites you want to permit relaying through your site, as well as any sites you use to access your server.

1. Send yourself an e-mail. If sendmail is working, you will receive the message.
2. Edit your e-mail client configuration — temporarily change your return e-mail address to that of a spammer that appears in your /etc/spammers.txt file (or temporarily enter your own return address in /etc/spammers.txt). Now send yourself another e-mail. This e-mail should be blocked.
3. Remember to put back your correct return e-mail address.
4. If your Web server and your internet access service have separate domain names, you must put the domain name of your access service in /etc/relaydomains.txt in order to be able to send e-mail. Be sure to make this entry and test your ability to send e-mail.
5. There is no easy way to test the /etc/spamdomains.txt file and code. The hard way is to temporarily enter the name of a site you have access to, and e-mail yourself from there. If all is well, this e-mail test will fail. Remember to remove the temporary entry from /etc/spamsites.txt.

• spammers.txt — e-mail addresses of known spammers
• spamdomains.txt — host and domain names of sites that permit spammers

These Pages Created and Maintained using   Arachnophilia.

Main Page

Home |

Programming Resources |

Anti-Spam |

* The Anti-Spam Home Page The Old Anti-Spam Home Page (archived)

Share This Page