How to use SpamProbe via sieve rules in Dovecot

spamprobe_sieve

This is a brief outline of how to take advantage of using only sieve scripts to manage spam via
`SpamProbe` and `Dovecot` IMAP services. First we assume there is a directory available for
global sieve scripts...

    [[ ! -d /usr/lib/dovecot/sieve ]] && mkdir -p /usr/lib/dovecot/sieve
    
then we add these rules to a Dovecot config file. I'll assume `/etc/dovecot/dovecot.conf` for simplicity...

    plugin {
      imapsieve_mailbox1_before = file:/usr/lib/dovecot/sieve/retrain-as-spam.sieve
      imapsieve_mailbox1_causes = COPY
      imapsieve_mailbox1_name = Spam
      imapsieve_mailbox2_before = file:/usr/lib/dovecot/sieve/retrain-as-good.sieve
      imapsieve_mailbox2_causes = COPY
      imapsieve_mailbox2_from = Junk
      imapsieve_mailbox2_name = *
      sieve = file:~/sieve;active=~/.dovecot.sieve
      sieve_after = /usr/lib/dovecot/sieve/spamprobe.sieve
      sieve_dir = ~/sieve
      sieve_execute_bin_dir = /usr/lib/dovecot/sieve
      sieve_extensions = +vnd.dovecot.debug +editheader
      sieve_global = /usr/lib/dovecot/sieve/
      sieve_global_extensions = +vnd.dovecot.execute
      sieve_plugins = sieve_imapsieve sieve_extprograms
    }

Next we create 3 sieve scripts and a symlink to the `/usr/bin/spamprobe` binary...

    cd /usr/lib/dovecot/sieve
    cat << EOS > retrain-as-good.sieve
    require ["vnd.dovecot.execute", "variables", "fileinto", "environment", "vnd.dovecot.debug"];
    if address :localpart :matches "delivered-to" "*" { set "localpart" "${1}"; }
    if address :domain :matches "delivered-to" "*" { set "domain" "${1}"; }
    execute :pipe :output "RESULT" "spamprobe" ["-d", "/home/u/${domain}/home/${localpart}/.spamprobe", "good"];
    EOS
    cat << EOS > retrain-as-spam.sieve
    require ["vnd.dovecot.execute", "copy", "variables", "fileinto", "environment", "vnd.dovecot.debug"];
    if address :localpart :matches "delivered-to" "*" { set "localpart" "${1}"; }
    if address :domain :matches "delivered-to" "*" { set "domain" "${1}"; }
    execute :pipe :output "RESULT" "spamprobe" ["-d", "/home/u/${domain}/home/${localpart}/.spamprobe", "spam"];
    EOS
    cat << EOS > spamprobe.sieve 
    require [ "variables", "fileinto", "envelope", "editheader", "vnd.dovecot.execute" ];
    if envelope :localpart :matches "to" "*" { set "localpart" "${1}"; }
    if envelope :domain :matches "to" "*" { set "domain" "${1}"; }
    execute :pipe :output "SCORE" "spamprobe" ["-c", "-d", "/home/u/${domain}/home/${localpart}/.spamprobe", "receive"];
    addheader :last "X-Spam" "${SCORE}";
    if header :matches "X-Spam" "SPAM*" { fileinto "Spam"; }
    EOS
    sievec retrain-as-good.sieve
    sievec retrain-as-spam.sieve
    sievec spamprobe.sieve
    ln -s /usr/bin/spamprobe
    systemctl restart dovecot

Then to set up a user we `su - someuser` and change dir to their virtual home dir where their
`Maildir` exists and "seed" a `.spamprobe` directory. If you do not have a ham/spam corpus handy
then you can use this one...

    wget https://renta.net/public/_etc_spamprobe.tgz
    tar xf _etc_spamprobe.tgz
    mv spamprobe .spamprobe
    chown UID:GID -R .spamprobe # where UID:GID is YOUR user and group ID
    spamprobe -d .spamprobe counts # to check all is well

And that is mostly it. Any incoming spam should end up in the `Spam` folder and any incorrectly
tagged messages (spam messages in your Inbox or good messages in your Spam folder) can simply
be dragged to or from the `Spam` folder to retrain the `SpamProbe` filtering database.