Configure SMTP in Docker container

Okay, I was running now

RAILS_ENV=production bundle exec rails c

irb(main):002:0> message = TestMailer.send_test("test@gmail.com")
Traceback (most recent call last):
        2: from app/mailers/test_mailer.rb:7:in `send_test'
        1: from lib/email/build_email_helper.rb:8:in `build_email'
ArgumentError (:arguments expected to be an Array of individual string args)

Also, this here does not work:

root@discourse-69c7f5475c-h9qf5:/opt/bitnami/discourse# RAILS_ENV=production bundle exec rails c message = TestMailer.send_test("test@gmail.com")
bash: syntax error near unexpected token `('

Am I doing something wrong here?