Vedere man maildropex.

#-------------------------------------------------------------------------
# $HOME/.mailfilter
#
# regex flags, used after the regex: /something/:b
# :h - header
# :b - body
# :D - distinguish between upper and lower case (default is to ignore case)
#-------------------------------------------------------------------------

# Configure for mbox, maildir, or mh
TYPE="maildir"

DEFAULT="$HOME/Maildir"

# Execute xfilter using this shell.
# Wrap commands into exception{} to deal with errors.
SHELL="/bin/sh"

MAILDIRMAKE="/usr/bin/maildirmake"

# Enable mail tracing.
#logfile "$HOME/mailfilter.log"

#-------------------------------------------------------------------------
# Filter the mail with ClamAV
#-------------------------------------------------------------------------
exception {
    xfilter "/usr/bin/sanitizer /etc/sanitizer.cfg"
}

#-------------------------------------------------------------------------
# Filter the mail with SpamAssassin
# spamc automatically skip messages greater than 512000 bytes.
#-------------------------------------------------------------------------
if ($SIZE < 256000)
{
    exception {
        xfilter "/usr/bin/spamc"
    }
}

#-------------------------------------------------------------------------
# Blackhole or move into subfolder messages tagged as SPAM.
#-------------------------------------------------------------------------
if (/^X-Spam-Flag: *YES/)
{
    exception {
        to "/dev/null"
        # Create Spam subfolder (little overhead if it exists).
        #`${MAILDIRMAKE} -f Spam "$DEFAULT"`
        #to "$HOME/Maildir/.Spam"
    }
}