5-A: WEBMAIL
I'll leave the software up to you.
I include Squirrelmail because it was on the qmailrocks guide and roundcube which is one of the most used (and I found it quite good)
For enabling HTTPS (which is quite recommendable) you have to do the following:
echo "NameVirtualHost *:443" >> /etc/apache2/ports.conf
a2enmod ssl
Then your virtual host file should look something like this
<VirtualHost *:443>
ServerAdmin noc@example.org
ServerName webmail.example.org
DocumentRoot /var/www/squirrelmail
ErrorLog /var/log/apache2/errores_squirrel
LogLevel warn
<IfModule mod_ssl.c>
SSLEngine on
SSLCertificateFile /etc/ssl/certs/ssl-cert-snakeoil.pem
SSLCertificateKeyFile /etc/ssl/private/ssl-cert-snakeoil.key
<FilesMatch "\.(cgi|shtml|phtml|php)$">
SSLOptions +StdEnvVars
</FilesMatch>
<Directory /usr/lib/cgi-bin>
SSLOptions +StdEnvVars
</Directory>
BrowserMatch "MSIE [2-6]" \
nokeepalive ssl-unclean-shutdown \
downgrade-1.0 force-response-1.0
BrowserMatch "MSIE [17-9]" ssl-unclean-shutdown
</IfModule>
</VirtualHost>