The talk presents a mail migration project at the University of Bonn where more than 60 000 mail accounts have been migrated from a monolithic proprietary mail system to a modular FOSS-based solution. The used components for the new setup include amongst others: * Postfix * Dovecot * Rspamd * SOGo * OpenLDAP * MariaDB Galera * KeyDB * keepalived * memcached

The presentation provides an insight into the motivation, planning, chosen migration approach, overcome difficulties and first operational experience with the new system. Finally an outlook is given on upcoming planned developments.