How to set up smtp server on postfix using smtp.gmail.com as relay?

Question

Email

Hello
At the moment I have the following scheme for sending email:

mydomain.com( server1 ) -> smtp.gmail.com -> client

When requesting to recover a password, the client receives the IP address of the sender (which is the application server) in the body of the letter. Therefore, in order to anonymize the server with the application, I see the need to configure an smtp proxy. To do this, I want to set up the following scheme:

mydomain.com( server1 ) -> smtp.myproxy.com postfix relay( server2 ) -> smtp.gmail.com  -> client

Those. so that smtp.gmail.com is upstream postfix.
I set up the relay . Local sending from server2 works.
How now to raise an SMTP server on Postfix listening to all addresses (0.0.0.0) under a certain domain?
I apologize for the noob questions, I'm just swimming in the subject of mail servers because I have no practice
Thank you
Part of the answer:
In the file:
cat /etc/postfix/main.cf
added:

inet_interfaces = all
mynetworks = 1.1.1.1/32,127.0.0.1/32

Now I can send mail remotely with the command:

mailx -S smtp=<postfix-server-ip> -r <sender-email> -s subfff -v <receiver-email>

Answer 1

Answer:
In file:
added:

inet_interfaces = all
mynetworks = 1.1.1.1/32,127.0.0.1/32

Now I can send mail remotely with the command:

mailx -S smtp=<postfix-server-ip> -r <sender-email> -s subfff -v <receiver-email>