Initially I was using inbuilt filtering system from gnus. Since I run emacs all the time on my machine and the filtering mechanism was interfering with my editing task, I thought of decoupling the same from Gnus. Google helped me to find imapfilter which is a very powerful tool.

Getting imapfiler

You can download the software from here http://imapfilter.hellug.gr/.

Installing

You can compile and install the program from the sources by typing:

tar -zxvf imapfilter-x.y.z.tar.gz
cd imapfilter-x.y.z
make
make install

Configuring

imapfilter uses lua as extension language. Here is an example ~/.imapfilter/config.lua
You can configure multiple mail accounts. Since I have only one
non-gmail account I have not tried that. The syntax is self explanatory.

• Define an account like this.

    account1 = IMAP {
    server = 'your.exchage.server.com',
    username = 'username',
    password = 'reallysecret',
    ssl = 'ssl3'
}

• Filter messages based on different header fields like this.

msgs = account1.INBOX:contain_field('To', 'x-mailing-list@mail.com')
msgs = account1.INBOX:contain_field('Subject', 'Joke')
msgs = account1.INBOX:contain_field('From', 'support@bank.com')

You can use complex filters like

       msgs = account1.INBOX:contain_field('To', 'y-mailing-list@mail.com') +
       account1.INBOX:contain_field('Cc', 'y-mailing-list@mail.com')

• Perform an action on the filters messages

account1.INBOX:move_messages(account1['x-mailing-list'], msgs)

• If we combine everything into a function.

    function sortMail()
    options.timeout = 120
    options.subscribe = true                                                    

    account1 = IMAP {
        server = 'your.exchage.server.com',
        username = 'username',
        password = 'reallysecret',
        ssl = 'ssl3'
    }                                                                           

    msgs = account1.INBOX:contain_field('To', 'x-mailing-list@mail.com')
    account1.INBOX:move_messages(account1['x-mailing-list'], msgs)
    msgs = account1.INBOX:contain_field('Subject', 'Joke')
    account1.INBOX:move_messages(account1['jokes'], msgs)
    msgs = account1.INBOX:contain_field('From', 'support@bank.com')
    account1.INBOX:move_messages(account1['bank'], msgs)

    msgs = account1.INBOX:contain_field('To', 'y-mailing-list@mail.com') +
           account1.INBOX:contain_field('Cc', 'y-mailing-list@mail.com')
    account1.INBOX:move_messages(account1['y-mailing-list'], msgs)
end                                                                             

become_daemon(300, sortMail)

Now we have a simple complete imapfilter config.lua. This file should
reside in ~/.imapfilter/ folder. This is the default location.

Executing imapfilter

Just run the following command. The option -l is used to specify log file.

imapfilter -l /tmp/imapfilter.log

Trouble

I had one issue with imapfilter so far. Sometimes the program terminates because of some protocol handling issue with the exchange server. So I have a script watch_imapfilter.sh added to crontab to monitor imapfilter process.

#!/bin/sh                                                                       

result=`pgrep imapfilter`
if [ $result ]
then
        echo "imapfilter is already running"
else
        echo "imapfilter is not running"
        echo "Starting imapfilter...."
        /usr/local/bin/imapfilter -l /tmp/imapfilter.log
fi

And the crontab entry looks like this.

# m h  dom mon dow   command
*/1 * * * *          /home/noorul/bin/watch_imapfilter.sh >/dev/null 2>&1

Further reading

The imapfilter and imapfilter_config manual pages are available online.