Postfix Configuration - Custom Mail Route

If running Postfix in a container the commands below can be used to configure a custom mail route for a domain. This will allow the Postfix server to delivery emails for the configured domain to a specific MTA/mail server instead of using the domains MX record.

1. Access the container

docker exec -it <container_id> /bin/bash

2. Open the transport map

nano /etc/postfix/transport

3. Add the custom route using the syntax below to the transport file, save and exit

xyz.com smtp:[192.0.2.1]

4. Create a hash database of the transport map

postmap /etc/postfix/transport

5. Open Postfix config file

nano /etc/postfix/main.cf

6. Add the transport map hash to the config

transport_maps = hash:/etc/postfix/transport

7. Restart Postfix

postfix reload

If you need to add additional domains in the future, you will need to rehash the map (Step 4) and then restart Postfix (Step 7). Steps 5 and 6 will not be needed.