Mailu

University team runs 10,000 Stalwart mailboxes on PostgreSQL and S3 storage

Operators running Stalwart for a 10,000-mailbox university keep settings in PostgreSQL and messages in S3 storage, so no mailbox sits on one machine's disk. Their mailcow and Mailu verdicts come from documentation, where failover means a cold standby or a shared ReadWriteMany volume.