Squirrelmail is open source webmail software, written in PHP and licensed under the GNU General Public License.
The email.uoa.gr project, which aims for a feature-rich and scalable mail system, is actively contributing code for the Squirrelmail project.
Whenever a single webmail machine is not adequate, a new machine can be added very easily. The only thing that must be changed on 'webmail2' should be the IP and the SSL certificate.
Such scalability also applies to other components of the mail system.
A special feature of the email solution is the implementation of "mailing lists" or "bulletin boards" as IMAP shared folders.
Squirrelmail's left frame has been modified to display not only these folders, but some information about them as well: mainly, a short textual description of the shared folder / bulletin board, and a small icon to post easily to a folder, provided the user has the appropriate permissions.
This makes for a complete, scalable and, most of all, RFC-defined groupware solution.