run

docker run --rm -d --name postfix \
-e MAILGUN_USER=postmaster@domain \
-e MAILGUN_PASS=xxxxxxxxx \
-e MAILGUN_RELAYHOST=smtp.mailgun.org \
fametec/postfix-mailgun:latest

docker-compose

version: '3.2'
#
### Services
#
services:
#
# MAILGUN
#
  relay:
    build: .
    image: fametec/postfix-mailgun:latest
    restart: unless-stopped
    container_name: relay
    ports:
     - "30025:25"
    environment:
     MAILGUN_USER: postmaster@XXXXXXXXXXXXXXXX
     MAILGUN_PASS: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
     MAILGUN_RELAYHOST: smtp.mailgun.org

testing

echo "Email Test" | mail -s "This is a simple test" contato@fametec.com.br