How to dockerise an mail service with docker?

I am working with docker technology.
I am proud to do somes good things with, but i’ am litle stucked right now.
If you could held me, i will be pleased.

Let me explain you. I have to create a webmail + mail service in my entreprise.
I have to use docker to do it.

I first started to do it in local.

So i got some docker images, like rainloop for webmail, and another image for postfix and dovecot and other things.

Here is my actual project state https://github.com/fab5741/docker-mailserver

So i can connect to my webmail, and send mails locally, in my domain. But i cant get out of my domain.

Do you have an idea on how to go out my network ?

Is it a simple postfix config ? or may i have to configure a dns in another docker container, and do the routing by myself ?

Thanks u for your attention !