I have Mailcow in a current Proxmox, its own Ubuntu 24 Server VM, standard setup including Internet DNS, except submission is LAN-only, it’s all behind a Watchguard firewall with appropriate rules. TLS/465 submission works, it hesitates a lot. STARTTLS/587 does not work, it freezes. I’m using Betterbird for testing. The only anomaly I’ve found is, Unbound fails self-tests, and when I get into the Unbound container, ‘dig’ tries IPv6 only by default at least, whereas nslookup succeeds using IPv4. This is a v6-inactive LAN for the most part, certainly all Internet connection is v4. Thoughts?