Functionality
Sieve is used to filter messages directly on the imap server. In this way, it can replace local mail filter rules in the user’s email agent. This is very useful, if more then one email agent is used – e.g. if the same server is used from different computers or operatint systems. In my case, the company notebook is Windows driven (using Thunderbird) and my workstation is running on linux using Evolution as a mail client. My mails are filtered by Sieve so I do not need to edit filter rules for each client.
Installation
The installation on Debian based systems is included in the Cyrus21 setup files. For an imap installation the following files are needed
- cyrus21-admin
- cyrus21-imapd
- cyrus21-common
- cyrus21-clients
Setup
The file /etc/service must contain the needed sieve setup
sieve 2000/tcp # Sieve mail filter daemon
The file /etc/cyrus.conf looks like
SERVICES {
# --- Normal cyrus spool, or Murder backends ---
# add or remove based on preferences
imap cmd="imapd -U 30" listen="moonworld.muehlencord.intra:imap" prefork=0 maxchild=100
imaplocal cmd="imapd -C /etc/imapd.conf.local" listen="localhost:imap" preforf=0 maxchild=100
# At least one form of LMTP is required for delivery
# (you must keep the Unix socket name in sync with imap.conf)
#lmtp cmd="lmtpd" listen="localhost:lmtp" prefork=0 maxchild=20
lmtpunix cmd="lmtpd" listen="/var/run/cyrus/socket/lmtp" prefork=0 maxchild=20
# ----------------------------------------------
# useful if you need to give users remote access to sieve
# by default, we limit this to localhost in Debian
sieve cmd="timsieved" listen="moonworld.muehlencord.intra:sieve" prefork=0 maxchild=100
sievelocal cmd="timsieved -C /etc/imapd.conf.local" listen="localhost:sieve" preforf=0 maxchild=100
# this one is needed for the notification services
notify cmd="notifyd" listen="/var/run/cyrus/socket/notify" proto="udp" prefork=1
# ----------------------------------------------
}
Activate the server including the Sieve support using the following command
/etc/init.d/cyrus21 restart
Creating user’s rules
The user rules are typed into an ascii file using your favorite editor. You can select what ever you want as the file name – e.g. rules.txt. There are different action, which can be perfomed on each single mail. Some of them require an external subroutine being called first. They are marke with a (*) in the table below.
- keep – keeps the message – it will be moved into the INBOX
- fileinto(*) – moves the message into a given subfolder. Example: fileInto “INBOX.Spam”
- discard – deletes the incomming email
- vacation (*) – sends an out of office reply
- redirect(*) – forwards the email to another email address
- reject – sends the email back to the sender. Example reject “Message to sender”
The subroutines are called by the require statement at the beginning of the file. Supported are the following statements
- require “fileinto”;
- require [“fileinto”, “vacation”]
If-Then-Else-Clause
The main part is the if-then-else block, each filterfile contains
if { }
elsif { }
else { }
Each single mail is processed by using the rule file. If the check constraint is true, the action is performed on the email. The last action should be the “keep” action – to tell sieve not to touch the email in any case.
Check constraints
The table below is just a selection of the possible fields.
address - from, to, cc, bcc - check emails address fields header - e.g. subject, date - any header field inside the email size - size of the email
Two or more checks can be combined using the allof of anyof aggregator functions. The syntax is
if anyof (
check1,
check2
)
{
action
}
Operators
:is - exact match :contains - partial match :matches - enables wildcards (*,?) and regular expressions :under or :above - compare to a value
You can use K,M or G as a short cut for kilobyte, megabyte or gigabyte for the above or under operators.
Deploying user’s rules
Each user can deploy is own rules on the server. The use writes a rule file, and uses the programm “sieveshell” to deploy it to the Sieve server.
% myhost: $ sieveshell localhost Connecting to localhost Please enter your password
After the user has connected he can use
put myfile.txt activate myfile.txt list myfile.txt
to load a new file, activate a file and double check which file are loaded and which one is activated.
Examples
moving mails from a mailinglist
## mailinglist linux@lug-owl.de
if header :contains "X-BeenThere" "linux@lug-owl.de" {
fileinto "INBOX.Linux.Lug-OWL";
stop;
}
reject large messages
if size :over 1M {
reject "Please do not send me large attachments.";
stop;
}