I've checked the FAQ and found that I can useyour service also as an outbound relay for my domain domain.com and example.co. I need to setup this service as I'm on a home internet IP and normally all of my emails are rejected due to that condition.

May you please provide me with the credentials to set up my postfix's /etc/postfix/sasl_passwd
[relay.dynu.com] relay@relay.yourdomain.com: <password>

I'm assuming this is an included with the store and forward service, so no extra cost, yes?.

Thanks in advance.

I found a Postfix tutorial at https://www.dynu.com/Resources/Tutorials/EmailServices/EmailServerSetup/How-to-configure-postfix-with-SMTP-relay. I would think outbound relay service is a separate service and it is not included with the email store/forward.