Después de configurar Discourse en una instalación estándar en mi Pi, terminó con:
+ /usr/bin/docker run --shm-size=512m -d --restart=always -e LANG=en_US.UTF-8 -e RAILS_ENV=production -e UNICORN_WORKERS=8 -e UNICORN_SIDEKIQS=1 -e RUBY_GC_HEAP_GROWTH_MAX_SLOTS=40000 -e RUBY_GC_HEAP_INIT_SLOTS=400000 -e RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR=1.5 -e DISCOURSE_DB_SOCKET=/var/run/postgresql -e DISCOURSE_DB_HOST= -e DISCOURSE_DB_PORT= -e LETSENCRYPT_DIR=/shared/letsencrypt -e DISCOURSE_FORCE_HTTPS=true -e LC_ALL=en_US.UTF-8 -e LANGUAGE=en_US.UTF-8 -e DISCOURSE_HOSTNAME=ndiscourse.obl.ong -e DISCOURSE_DEVELOPER_EMAILS=***************@gmail.com -e DISCOURSE_SMTP_ADDRESS=smtp.gmail.com -e DISCOURSE_SMTP_PORT=587 -e DISCOURSE_SMTP_USER_NAME=***************@gmail.com -e DISCOURSE_SMTP_PASSWORD=************** -e DISCOURSE_SMTP_DOMAIN=gmail.com -e DISCOURSE_NOTIFICATION_EMAIL=*************@gmail.com -e LETSENCRYPT_ACCOUNT_EMAIL=me@example.com -h raspberrypi-app -e DOCKER_HOST_IP=172.17.0.1 --name app -t -p 80:80 -p 443:443 -v /var/discourse/shared/standalone:/shared -v /var/discourse/shared/standalone/log/var-log:/var/log --mac-address 02:ee:d2:40:e1:0e local_discourse/app /sbin/boot
e3e6d64cbec56cdf8672ace7d60f60a2e843d2b590e443f9b09dd1ca8b58cb70
Seguramente el uso de un correo electrónico de Gmail no es la causa.
https://ndiscourseforum.obl.ong no parece estar funcionando.