How to add mail into docker compose ghost

How do I configure mail, transport, mail options, etc in docker compose?
It’s my first time using it so I need some help.

Basically how to add this into docker compose:
“mail”: {
“transport”: “SMTP”,
“options”: {
“service”: “Mailgun”,
“auth”: {
“user”: “”,
“pass”: “12312312312123”

The most common approach is setting them as environment variables:

Based on your example, it would look like this: