Howtoforge published a tutorial about setting up a mail server with PostfixAdmin on Debian 11.
How to Set Up a Mail Server with PostfixAdmin on Debian 11
PostfixAdmin is a free, open-source, and web-based interface used for managing Postfix mail server from the web browser. It allows you to add users, aliases, set a disk quota, add and remove domains from the web-based interface. It supports several database backends including PostgreSQL, MySQL, MariaDB, and SQLite. It can be integrated with Squirrelmail and Roundcube via plugins.