Insert these lines into `data/conf/postfix/main.cf`. "relayhost" does already exist (empty), just change its value. ``` relayhost = [your-relayhost]:587 smtp_sasl_password_maps = hash:/opt/postfix/conf/smarthost_passwd smtp_sasl_auth_enable = yes ``` Create the credentials file: ``` echo "your-relayhost username:password" > data/conf/postfix/smarthost_passwd ``` Run: ``` docker-compose exec postfix-mailcow postmap /opt/postfix/conf/smarthost_passwd docker-compose exec postfix-mailcow chown root:postfix /opt/postfix/conf/smarthost_passwd /opt/postfix/conf/smarthost_passwd.db docker-compose exec postfix-mailcow chmod 660 /opt/postfix/conf/smarthost_passwd /opt/postfix/conf/smarthost_passwd.db docker-compose exec postfix-mailcow postfix reload ``` ### Helper script There is a helper script `mailcow-setup-relayhost.sh` you can run to setup a relayhost. ``` bash Usage: Setup a relayhost: ./mailcow-setup-relayhost.sh relayhost port (username) (password) Username and password are optional parameters. Reset to defaults: ./mailcow-setup-relayhost.sh reset ```