Roundcube

wget -c http://ufpr.dl.sourceforge.net/sourceforge/roundcubemail/roundcubemail-0.2.1.tar.gz
tar zxvf roundcubemail-0.2.1.tar.gz
mv roundcubemail-0.2.1 /var/www/webmail
cd /var/www/webmail/config
cp db.inc.php.dist db.inc.php
cp main.inc.php.dist main.inc.php
cd ..
chown -R www-data temp logs
cp /home/arq/roundcube_logo.png /var/www/nkosi.org/webmail/skins/default/images/
cp /home/arq/favicon.ico /var/www/nkosi.org/webmail/skins/default/images/

em db.inc.php altera a linha 21 de acordo com as informações do seu banco de dados

mysql -u root -p
mysql > GRANT ALL PRIVILEGES ON roundcubemail.* TO roundcube@localhost IDENTIFIED BY 'suasenha';
mysql > create database roundcubemail;
mysql > use roundcubemail;
mysql > source SQL/mysql.initial.sql
mysql > quit

para compilar:

# apt-get install php-pear libmagic-dev php5-dev make php5-gd php5-mcrypt build-essential
# pecl install fileinfo
# echo "extension=fileinfo.so" | tee /etc/php5/conf.d/fileinfo.ini

instalando depedencias:

acesse http://localhost/webmail/installer/

em config/main.inc.php na linha 252

de

$rcmail_config['enable_installer'] = false;

para

$rcmail_config['enable_installer'] = true;