RFC 2505 (rfc2505) - Page 2 of 24


Anti-Spam Recommendations for SMTP MTAs



Alternative Format: Original Text Document



RFC 2505               Anti-Spam Recommendations           February 1999


1. Introduction

   This memo is a Best Current Practice (BCP) RFC.  As such it should be
   used as a guideline for SMTP MTA implementors to make their products
   more capable of preventing/handling spam.  Despite this being its
   primary goal, an intended side effect is to suggest to the
   sysadmin/Postmaster community which "anti spam knobs" an SMTP MTA is
   expected to have.

   However, this memo is not generally intended as a description on how
   to operate an SMTP MTA - which "knobs" to turn and how to configure
   the options. If suggestions are provided, they will be clearly marked
   and they should be read as such.

1.1. Background

   Mass unsolicited electronic mail, often known as spam(*), has
   increased considerably during a short period of time and has become a
   serious threat to the Internet email community as a whole. Something
   needs to be done fairly quickly.

   The problem has several components:

   o   It is high volume, i.e. people get a lot of such mail in their
       mailboxes.

   o   It is completely "blind", i.e. there is no correlation between
       the receivers' areas of interest and the actual mail sent out (at
       least if one assumes that not everybody on the Internet is
       interested in porno pictures and spam programs...).

   o   It costs real money for the receivers. Since many receivers pay
       for the time to transfer the mailbox from the (dialup) ISP to
       their computer they in reality pay real money for this.

   o   It costs real money for the ISPs. Assume one 10 Kbyte message
       sent to 10 000 users with their mailboxes at one ISP host; that
       means an unsolicited, unexpected, storage of 100 Mbytes.  State
       of the art disks, 4 Gbyte, can take 40 such message floods before
       they are filled. It is almost impossible to plan ahead for such
       "storms".

   o   Many of the senders of spam are dishonest, e.g. hide behind false
       return addresses, deliberately write messages to look like they
       were between two individuals so the spam recipient will think it
       was just misdelivered to them, say the message is "material you





Lindberg                 Best Current Practice