• Server: https://www.hetzner.de/dedicated-rootserver/matrix-ex
• KVM with Proxmox VE (GUI): https://www.proxmox.com/de/proxmox-ve
• Proxmox Mail Gateway: https://www.proxmox.com/de/proxmox-mail-gateway
• Dokku: https://github.com/dokku/dokku

Pros:

• Snapshots for VM Backup
• flexbile

Cons:

• Requires a server admin!
• Own backups
• Not scalable - just a single server