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