This question here remains open. It looks like mynetworks is set to 192.168.2.124/24 and 10.8.0.1/24 (beside this, defining the last octet doesn’t make any sense - 192.168.2.0/24 10.8.0.0/24 would be correct). This allows IPs 192.168.2.0-192.168.2.255 and 10.8.0.0-10.8.0.255 to send unlimited emails without any restrictions.
As this is rather a security concern and allow potentially any IPs/services in that range to uncontrollably send spam (what we see here), these values are NOT set by default. Use mailboxes with authentication to send emails.
Also this remained unanswered:
pkernstock Is mailcow “directly” in the network, or behind some NAT?
If mailcow has a wrong configured NAT and using a IP from this range, it can lead to a open relay.
