Anarcat's
"procmail considered harmful" post
convinced me to get my act together and finally migrate my venerable procmail based setup to sieve.
My setup was nontrivial, so I migrated with an intermediate step in which sieve
scripts would by default pipe everything to procmail, which allowed me to
slowly move rules from
procmailrc to sieve until nothing remained in
procmailrc.
Here's what I did.
Literature review
https://brokkr.net/2019/10/31/lets-do-dovecot-slowly-and-properly-part-3-lmtp/
has a guide quite aligned with current Debian, and could be a starting point to
get an idea of the work to do.
https://wiki.dovecot.org/HowTo/PostfixDovecotLMTP is way more terse, but
more aligned with my intentions. Reading the former helped me in understanding
the latter.
https://datatracker.ietf.org/doc/html/rfc5228 has the full Sieve syntax.
https://doc.dovecot.org/configuration_manual/sieve/pigeonhole_sieve_interpreter/
has the list of Sieve features supported by Dovecot.
https://doc.dovecot.org/settings/pigeonhole/ has the reference on Dovecot's
sieve implementation.
https://raw.githubusercontent.com/dovecot/pigeonhole/master/doc/rfc/spec-bosch-sieve-extprograms.txt
is the
hard to find full reference for the functions introduced by the
extprograms plugin.
Debugging tools:
- doveconf to dump dovecot's
configuration to see if what it understands matches what I mean
- sieve-test
parses sieve scripts:
sieve-test file.sieve /dev/null is a quick and dirty
syntax check
Backup of all mails processed
One thing I did with procmail was to generate a monthly mailbox with all
incoming email, with something like this:
BACKUP="/srv/backupts/test- date +%Y-%m-d .mbox"
:0c
$BACKUP
I did not find an obvious way in sieve to create montly mailboxes, so I
redesigned that system using Postfix's
always_bcc
feature, piping everything to an archive user.
I'll then recreate the monthly archiving using a
chewmail script that I can simply run
via cron.
Configure dovecot
apt install dovecot-sieve dovecot-lmtpd
I added this to the local dovecot configuration:
service lmtp
unix_listener /var/spool/postfix/private/dovecot-lmtp
user = postfix
group = postfix
mode = 0666
protocol lmtp
mail_plugins = $mail_plugins sieve
plugin
sieve = file:~/.sieve;active=~/.dovecot.sieve
This makes Dovecot ready to receive mail from Postfix via a lmtp unix socket
created in Postfix's private chroot.
It also activates the sieve plugin, and uses
~/.sieve as a sieve script.
The script can be a file or a directory; if it is a directory,
~/.dovecot.sieve will be a symlink pointing to the
.sieve file to run.
This is a feature I'm not yet using, but if one day I want to try
enabling UIs
to edit sieve scripts,
that part is ready.
Delegate to procmail
To make sieve scripts that delegate to procmail, I enabled the
sieve_extprograms plugin:
plugin
sieve = file:~/.sieve;active=~/.dovecot.sieve
+ sieve_plugins = sieve_extprograms
+ sieve_extensions +vnd.dovecot.pipe
+ sieve_pipe_bin_dir = /usr/local/lib/dovecot/sieve-pipe
+ sieve_trace_dir = ~/.sieve-trace
+ sieve_trace_level = matching
+ sieve_trace_debug = yes
and then created a script for it:
mkdir -p /usr/local/lib/dovecot/sieve-pipe/
(echo "#!/bin/sh'; echo "exec /usr/bin/procmail") > /usr/local/lib/dovecot/sieve-pipe/procmail
chmod 0755 /usr/local/lib/dovecot/sieve-pipe/procmail
And I can have a sieve script that delegates processing to procmail:
require "vnd.dovecot.pipe";
pipe "procmail";
Activate the postfix side
These changes switched local delivery over to Dovecot:
--- a/roles/mailserver/templates/dovecot.conf
+++ b/roles/mailserver/templates/dovecot.conf
@@ -25,6 +25,8 @@
+auth_username_format = %Ln
+
diff --git a/roles/mailserver/templates/main.cf b/roles/mailserver/templates/main.cf
index d2c515a..d35537c 100644
--- a/roles/mailserver/templates/main.cf
+++ b/roles/mailserver/templates/main.cf
@@ -64,8 +64,7 @@ virtual_alias_domains =
-mailbox_command = procmail -a "$EXTENSION"
-mailbox_size_limit = 0
+mailbox_transport = lmtp:unix:private/dovecot-lmtp
Without
auth_username_format = %Ln dovecot won't be able to understand
usernames sent by postfix in my specific setup.
Moving rules over to sieve
This is mostly straightforward, with the luxury of being able to do it a bit at
a time.
The last tricky bit was how to call
spamc from sieve, as in some situations I
reduce system load by running the spamfilter only on a prefiltered selection of
incoming emails.
For this I enabled the
filter directive in sieve:
plugin
sieve = file:~/.sieve;active=~/.dovecot.sieve
sieve_plugins = sieve_extprograms
- sieve_extensions +vnd.dovecot.pipe
+ sieve_extensions +vnd.dovecot.pipe +vnd.dovecot.filter
sieve_pipe_bin_dir = /usr/local/lib/dovecot/sieve-pipe
+ sieve_filter_bin_dir = /usr/local/lib/dovecot/sieve-filter
sieve_trace_dir = ~/.sieve-trace
sieve_trace_level = matching
sieve_trace_debug = yes
Then I created a filter script:
mkdir -p /usr/local/lib/dovecot/sieve-filter/"
(echo "#!/bin/sh'; echo "exec /usr/bin/spamc") > /usr/local/lib/dovecot/sieve-filter/spamc
chmod 0755 /usr/local/lib/dovecot/sieve-filter/spamc
And now what was previously:
:0 fw
/usr/bin/spamc
:0
* ^X-Spam-Status: Yes
.spam/
Can become:
require "vnd.dovecot.filter";
require "fileinto";
filter "spamc";
if header :contains "x-spam-level" "**************"
discard;
elsif header :matches "X-Spam-Status" "Yes,*"
fileinto "spam";
Updates
Ansgar mentioned that it's possible to replicate the monthly mailbox using the
variables and
date
extensions, with a hacky trick from the extensions' RFC:
require "date"
require "variables"
if currentdate :matches "month" "*" set "month" "$ 1 ";
if currentdate :matches "year" "*" set "year" "$ 1 ";
fileinto :create "$ month -$ year ";
Among my collection of PC hardware, I have a few rarities whose netboot implementation predates PXE. Since I recently managed to configure dnsmasq as a potent TFTP and PXE server, I figured that I'd try chainloading iPXE via BOOTP options. This required preparing a boot image using antiquated tools:
The following contributors got their Debian Developer accounts in the last two months:
I ve spent a bit of time playing with
My 
Ten years ago 
Like many I use 
I have uploaded most of my Machine Learning lecture to YouTube.
The slides are in English, but the audio is in German.
Some very basic contents (e.g., a demo of standard k-means clustering) were left out from this advanced class,
and instead only a link to recordings from an earlier class were given. In this class, I wanted to focus
on the improved (accelerated) algorithms instead. These are not included here (yet).
I believe there are some contents covered in this class you will find nowhere else (yet).
The first unit is pretty long (I did not split it further yet). The later units are shorter recordings.
ML F1: Principles in Machine Learning
screenshot showing power consumption of server
What I loved the most about Sikkim can t be captured on cameras. It can t be taped since it would be intrusive and it can t be replicated because it s unique and impromptu. It could be described, as I attempt to, but more importantly, it s something that you simply have to experience to know.
Now I first heard about this from a friend who claimed he d been offered free rides and Tropicanas by locals after finishing the Ladakh Marathon. And then I found 
