Colaboração: Rubens Queiroz de Almeida
Data de Publicação: 07 de Novembro de 1997
Spamming, ou a prática de se enviar numerosas mensagens anunciando
produtos comerciais, é a atual praga da Internet. É raro o dia em
que não recebo mensagens de alguém anunciando algo ou tentando
ensinar como ganhar dinheiro rápido.
O autor do servidor de listas, petidomo, escreveu um pacote
chamado mapSoN, que provê mecanismos para filtrar possíveis mensagens
Em anexo, segue o documento descritivo do programa.
O pacote e toda a documentação podem ser encontrados em
mapSoN: How does it work?
Unfortunately, the times when you could read your mail without any
filtering mechanisms seems to be over. Over the years, the number of
unsolicted commercial e-mails I receive per day has increased
dramatically. Today the average for me personally is something like
15(!) spam mails per day. What means, that I can hardly afford not to
read my mail for several consequetive days, or I'll have to wade
through a hundred of them, trying to find any <em>real mail</em> that
someone might have sent me.
So I decided that the time was ripe to change that. Unfortunately, the
filter mechanisms in existance today are not too sophisticated. Most
spam filtering tools I've seen so far are based on procmail, or a
similar tool, and use a list of keywords or addresses to drop unwanted
junk mail. While this might be nice to filter mail from known spam
domains like "cyberpromo.com", or "bulkmail.com", it won't catch most
of the spam one receives, because the addresses are faked, the headers
are manipulated and the contents of the mail itself is not
That's why I wrote mapSoN, which combines the keyword-filtering
mechanism with an, in my humble opinion, pretty good algorithm to keep
unwanted mail out of your folder.
mapSoN must be installed as filter program for your incoming mail,
usually by adding an appropriate entry to your $HOME/.forward file.
This means that mapSoN will get all your incoming mail and it will
decide whether or not to actually deliver it to your mailbox.
To do that, it uses three criteria. First of all, an user defined
ruleset is checked against the mail. If any keywords or patterns
match, the mail will be dealt with according to your wishes. This is
useful to drop some sender's mail completely, or to sort mail into
different mail folders.
If no rule matches the mail, mapSoN will check whether the mail is a
reply to an e-mail you sent, or whether it is a reply to a USENET
posting of yours. If it is, the mail will always be delivered.
If no signs of a reply-mail can be found, mapSoN will check whether
the sender stated in the <code>From:</code> header has sent you mail
before. If he has, the mail will pass. If this is the first time you
receive an e-mail from this address, though, mapSoN will delay the
delivery of the mail and spool it in your home directory. Then it will
send a short notice to the address the mail comes from, which may look
From: Peter Simons <email@example.com><br>
Subject: [mapSoN] Request for Confirmation
a few seconds ago I have received your electronic mail. I notice that
this is the first time you're trying to contact me via e-mail, and I
have a little procedure set up that protects me from unwanted junk
mail. This is why the mapSoN tool has delayed the delivery until it
receives a confirmation from you, by which you certify that you're NOT
sending me any unsolicted commercial stuff.
To confirm this, simply reply to this automatic e-mail and make sure
you include the following line in your reply:
You may quote the line, if that's more comfortable for you, the mapSoN
tool will recognize the confirmation anyway.
I am sorry for the extra effort, but unfortunately the amount of junk
mail I receive has made this preparative necessary. My tool keeps
track of who has sent me e-mail before and you won't see this notice
You can customize the mail text according to your wishes, preferred
language or personal taste of spelling, this is just the default text.
The person who tried to contact you will then reply to this "request
for confirmation", citing the cookie stated in the mail. When your
mapSoN receives this confirmation mail, it will deliver the spooled
mail into your folder. Furthermore, the address will be added to the
database, so that mail from this person will pass directly in future.
If no confirmation mail arrives within a certain time, mapSoN can
either delete the spooled mails, or send them to a special folder, or
whatever you prefer.
The mechanism is simple but efficient: Somebody who replies to an
e-mail or an USENET posting of your, will have his e-mail delivered to
you immediately. Somebody who knows you already and has exchanged
e-mail with you before, will also not notice any delays.
Somebody who sends you an e-mail for the first time, will have the
slight inconvenience of having to reply the request for confirmation
once, what can be automated, by the way, using procmail or a similar
filter. Spammers won't be able to confirm the request mail, though,
because they almost always use a faked, non-existant address, so the
request for confirmation won't reach them.
That's how it works.