mapSoN is an anti-spam system that uses an
approach which is entirely different than other
systems. Instead of trying to recognize spam by
the IP address of the SMTP dialog's peer or by
certain patters in the mail's body, it uses the
sender's email address to decide whether the
e-mail is delivered to your mailbox or not: Any
email that comes from a "known" address may pass,
but any email that comes from an email address
seen for the first time needs special confirmation
before it may pass. "Special confirmation" means
that mapSoN will generate an MD5 checksum of the
to-be-confirmed email and store the email in a
temporary spool directory. Then it sends a request
for confirmation to the address from which the
mail was coming. In this request, it will include
the MD5 checksum and ask the recipient to reply
back and to quote that MD5 hash. Once it sees that
MD5 hash again, it considers that a confirmation
of the original email, delivers the deferred email
from the spool to your mailbox, and adds the
sender's address to the database of known
addresses, so that the next time he tries to
contact you, his mail will pass through
immediately. This heuristic catches almost any
spam email, because spammers have to fake their
sender addresses in order to avoid being held
responsible for their abuse. Hence, their address
will most likely not be in the database of known
addresses, nor will they ever receive the request
for confirmation email.
