Docker/Omnibus configuration (SMTP)

I’m doing a trial of Gitlab-CE via the docker container for a client and am trying to get email working under AWS SES. I’m passing the following in $GITLAB_OMNIBUS_CONFIG:

      "gitlab_rails['smtp_enable']"  = "true";
      "gitlab_rails['smtp_address']" = "";
      "gitlab_rails['smtp_port']" = "587";
      "gitlab_rails['smtp_user_name']" = "...sekrit...";
      "gitlab_rails['smtp_password']" = "...other_sekrit...";
      "gitlab_rails['smtp_domain']" = "";
      "gitlab_rails['smtp_authentication']" = "login";
      "gitlab_rails['smtp_enable_starttls_auto']" = "true";          
      "gitlab_rails['gitlab_email_display_name']" = "GitLab";
      "gitlab_rails['gitlab_email_reply_to']" = "";
      "gitlab_rails['gitlab_email_from']" = "";

Yep, all of that (and more), but the logs are showing:

==> /var/log/gitlab/sidekiq/current <==
2017-07-23_08:31:14.37839 sh: 1: /usr/sbin/sendmail: not found

And email is not being sent. Poking around the container I don’t see any of the above values in gitlab-test:/opt/gitlab/embedded/service/gitlab-rails/config/config.yml (which is where it looks like those values should end up).

What am I missing? Got any good clues?

Same problem