reject email

we have a Synology Mail Plus Server running on a DS1621+. Mainly to get independent from mail providers and ensure confidentiality. Proxmox Mail Gateway runs as a virtual machine on the same. So far it worked well, but now we are running in severe problems. Emails from Banks, insurance...

Hello, I use Proxmox Mail Gateway in front of a primary email server. When emails are sent to over quota mailbox on primary email server, I want to reject them. I wonder why Proxmox Mail Gateway reject email to over quota mailbox with this maibox but queue email with other over quota maibox...