diff --git a/openproject/.env.example b/openproject/.env.example
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--- /dev/null
+++ b/openproject/.env.example
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+##
+# All environment variables defined here will only apply if you pass them
+# to the OpenProject container in docker-compose.yml under x-op-app -> environment.
+# For the examples here this is already the case.
+#
+# Please refer to our documentation to see all possible variables:
+#   https://www.openproject.org/docs/installation-and-operations/configuration/environment/
+#
+OPENPROJECT_DOMAIN=
+OPENPROJECT_TAG=
+OPENPROJECT_HTTPS=
+OPENPROJECT_HOST__NAME=
+OPENPROJECT_PORT=
+OPENPROJECT_IMAP_ENABLED=false
+OPENPROJECT_POSTGRES_USER=
+OPENPROJECT_POSTGRES_PASSWORD=
+OPENPROJECT_POSTGRES_DB=
+OPENPROJECT_RAILS_MIN_THREADS=
+OPENPROJECT_RAILS_MAX_THREADS=
+OPENPROJECT_OPDATA=