System: 12.2 RELEASE amd64 with 2 ethernet interfaces both with IPv4 addresses but IPv6 disabled; loopback interface still has IPv4 and IPv6. Port installed as package (emailrelay-1.9_6). Problem: any attempt to configure an interface with only an IPv4 address for the --listen option results in: (for IPv4 address) emailrelay: error: invalid ip address string: invalid format: 192.168.10.2 emailrelay: exception: invalid ip address string: invalid format: 192.168.10.2 (for interface name) emailrelay: error: invalid ip address string: invalid format: em0 emailrelay: exception: invalid ip address string: invalid format: em0 using "emailrelay --interface <address> --port 10025 --as-proxy localhost 25" If the interface isn't specified so emailrelay should listen on all interfaces for port 10025 (i.e. "emailrelay --port 10025 --as-proxy localhost:25"), sockstat reports: daemon emailrelay <pid> 3 tcp6 *:10025 *:* which suggests that emailrelay is only listening on IPv6 addresses as proto would be tcp46 if listening on both -4 and -6 addresses. PR 204126 seems to have been related but a long time ago. I note from the port commit log that the IPv6 configuration was changed relatively recently. The emailrelay documentation suggests that mixed IPv4 & IPv6 operation should be supported.