setup.md.
This example uses MailGun... don't try to use Google / G Suite, it's painful and rarely works.
...
environment:
GITLAB_OMNIBUS_CONFIG: |
...
gitlab_rails['smtp_enable'] = true
gitlab_rails['smtp_domain'] = 'mailgun.example.com'
gitlab_rails['smtp_address'] = 'smtp.mailgun.org'
gitlab_rails['smtp_port'] = 465
gitlab_rails['smtp_tls'] = true
gitlab_rails['smtp_enable_starttls_auto'] = false
gitlab_rails['smtp_authentication'] = 'login'
gitlab_rails['smtp_user_name'] = 'gitlab@mailgun.example.com'
gitlab_rails['smtp_password'] = 'XXX'
...
...
docker exec -it ${CONTAINER} gitlab-rails console
ruby tab="gitlab-rails console" Notify.test_email('${RECIPIENT_EMAIL}', 'TEST FROM GITLAB', 'HELLO').deliver_now