Jam.py Postfix Aliases - Web App to manage only Postfix Aliases with a LARGE number of managed Domains (>hundreds).
Postfix Admin - Postfix Admin is a web based interface used to manage mailboxes, virtual domains and aliases.
Modoboa - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.
mailcow - An open source mailserver suite.
NeutronMail - Self-hosted server for the ProtonMail client.
Ratuus - RATUUS is an easy to use, web based system for administration of POSTFIX virtual domains and users