Carmarthenshire county Welsh council, UK, uses Debian GNU / Linux for 150 schools, 30,000 students e-mail.
"A Welsh council has introduced an open-source email system covering
more than 150 schools with around 30,000 users."
"Carmarthenshire  county council  moved to open source for the
schools’ email system, migrating from a POP3 email system provided by
its in-house IT development centre to an IMAP system, based on the
open-source OpenLDAP protocol."
"The use of open source, with no software licence fees, also offers the
council a cost saving."
"The Carmarthenshire email system now gives school children and teachers
access to one of three different versions of the webmail client,
tailored according to age. All users have access to the webmail client
in both English and Welsh."
"The system is built on a highly scalable hosting platform based on the
Debian Linux distribution. "
Andre Felipe Machado