Ubuntu – Dovecot – Unable to receive mail – Fatal: Plugin ‘sieve’ not found

Struggling to Dovecot/Postfix set up on Ubuntu 11.10, Dovecot version: 2.0.13, Postfix version: 2.8.5

I can send outbound mail using the mailx command, but I can neither receive mail or send mail from SMTP.

I get this error from my dovecot-deliver.log:

2011-10-16 16:46:08 lda: Fatal: Plugin 'sieve' not found from directory /usr/lib/dovecot/modules

When I look in that directory there aren't any files referencing sieve at all so I'm not sure if there was a problem with the install and for some reason it didn't get added.

I've mostly followed this guide: http://library.linode.com/email/postfix/dovecot-mysql-ubuntu-10.10-maverick

I realise it is for 10.10 and not 11.x so possibly there are some differences there that are causing problems.

Below is my dovecot.conf:

protocols = imap imaps pop3 pop3s
log_timestamp = "%Y-%m-%d %H:%M:%S "
mail_location = maildir:/home/vmail/%d/%n/Maildir

ssl_cert_file = /etc/ssl/certs/dovecot.pem
ssl_key_file = /etc/ssl/private/dovecot.pem

namespace private {
    separator = .
    prefix = INBOX.
    inbox = yes
}

protocol lda {
    log_path = /home/vmail/dovecot-deliver.log
    auth_socket_path = /var/run/dovecot/auth-master
    postmaster_address = postmaster@jamesrwhite.co.uk
    mail_plugins = sieve
}

protocol pop3 {
    pop3_uidl_format = %08Xu%08Xv
}

auth default {
    user = root

    passdb sql {
        args = /etc/dovecot/dovecot-sql.conf
    }

    userdb static {
        args = uid=5000 gid=5000 home=/home/vmail/%d/%n allow_all_users=yes
    }

    socket listen {
        master {
            path = /var/run/dovecot/auth-master
            mode = 0600
            user = vmail
        }

        client {
            path = /var/spool/postfix/private/auth
            mode = 0660
            user = postfix
            group = postfix
        }

    }

}

Would really appreciate any thoughts as I've run out of ideas.