Hi James,
You might also need to create two outgoing ports, at least this is what I did when having to configure a system with two incoming email ports for two different clients
icm/server_port_2 = PROT=SMTP,PORT=25000,TIMEOUT=180
icm/server_port_3 = PROT=SMTP,PORT=25001,TIMEOUT=180
is/SMTP/virt_host_0 = *:25000;
is/SMTP/virt_host_1 = *:25001;
Regards