1. Login to console via SSH
2. Edit Postfix configuration file:
[for NXS and MHD device type:]
nano /etc/postfix/main.cf
[for NPE device type:]
nano /mnt/nand-user/postfix/etc/postfix/main.cf
3. Change line:
proxy_interfaces = [your external IP address]
4. Exit with CTRL+X, confirm y and and enter
5. Reload postfix configuration with:
[for NXS and MHD device type:]
service postfix reload
[for NPE device type:]
postfix reload