Merge branch 'postfix' into 'master'

README.md

roles/api/tasks/main.yml

roles/discourse/tasks/main.yml

roles/docker/tasks/main.yml

roles/email/files/00_local

roles/email/files/30_exim4-config_discourse

roles/email/files/450_exim4-config_discourse

roles/email/files/check_rcpt_local_acl

roles/email/files/discourse-smtp-fast-rejection

roles/email/files/discourse-smtp-rcpt-acl

roles/email/files/receive-mail

roles/email/tasks/main.yml

roles/email/templates/transport.j2

roles/email/templates/update-exim4.j2