The Annoyance Filter.pdf - Fourmilab

§7 ANNOYANCE-FILTER OPERATING A POP3 PROXY SERVER 13
7. Operating a POP3 proxy server.
On systems where it’s inconvenient or impossible to interpose annoyance−filter to filter incoming mail,
you may be able to use annoyance−filter as a proxy server for the “Post Office Protocol” used to deliver
mail from your mail host.
The program you use to read E-mail, for example, Netscape, Mozilla, or Microsoft Outlook, normally retrieves
messages from a mail server using Post Office Protocol as defined by Internet RFC 1939. annoyance−filter
has the ability to act as a proxy for this protocol, running on your local machine, and filtering messages
received from your mail server to classify them as legitimate mail or junk. Let’s assume you currently receive
incoming mail from a POP server at site mail.myisp.net. Once you’ve created a fast dictionary from
your collection of legitimate and junk mail, you can establish a proxy server directed at that site with the
command:
annoyance−filter --fread fdict.bin --pop3server mail.myisp.net
Now you need only configure your mail program to request incoming mail from your local machine (usually
called “localhost”) on the default proxy port of 9110. (You can change the proxy port with the −−pop3port
option if required.)
Messages retrieved through the proxy server will be annotated with annoyance−filter’s
X−Annoyance−Filter−Classification header item, which may be tested in your mail client’s filtering
rules to appropriately dispose of the message.
POP3 proxy server support is primarily intended for an individual user running on a platform which
doesn’t permit programmatic filtering of incoming mail. The proxy server is, however, completely general
and can support any number of individual mailboxes on a mail server, but with only a single dictionary
common to all mailboxes. Since accurate mail classification depends upon individual per-user dictionaries,
this is a capability best undeployed.
If you’re installing a POP3 proxy server on a Windows machine, you may wish to create a “.pif” file to
launch the program from the directory in which it resides with the correct options. A skeleton pop3proxy.pif
file is included in the Windows distribution archives which you can edit to specify parameters appropriate
for your configuration. (To edit the file, right click on it in Explorer and select the “Properties” item from
the pop-up menu.)