1 files changed, 67 insertions, 0 deletions
diff --git a/configs/system-integration/systemd/README.md b/configs/system-integration/systemd/README.md
new file mode 100644
index 000000000..5ac8e0af7
--- /dev/null
+++ b/configs/system-integration/systemd/README.md
@@ -0,0 +1,67 @@
+# System Unit Examples for Exim
+
+This directory contains several examples for Systemd units to manage an Exim installation.
+There is room for improvement, so please share your ideas or setups that are proven to work
+in your environment.
+
+All the service units try to protect the system from unintentional
+writes to locations outside of Exim's spool, and log directories.  You
+may need to override specific settings, we recommend using Systemd's
+override mechanism.
+
+## Daemon
+
+This is best suited for *average to high traffic systems*, as it engages
+all built-in Exim facilities, as queue runner management, and system load
+depended message processing.
+
+It starts the Exim main process. This process listens on the ports
+configured in the _runtime configuration_, and supervises all other
+activities, including management of queue runner startup (`exim -odf
+-q...`).
+
+For regular maintenance tasks (log rotation, database cleanup)
+additional units are required.
+
+## Socket
+
+This is best suited for *low traffic* systems, which experience a
+message *burst* from time to time. Regular desktop, and edge systems fit this
+pattern.
+
+Exim's start is delayed until the first connection. Once a connection is
+initiated, Exim starts a listener on the port configured in the [systemd
+socket unit](./socket/exim.socket) and waits for more connections, and exits after being idle
+(`exim -bw...`).
+
+Additional [_queue runner_ timer and service units](#queue-runner) are required.
+
+For regular maintenance tasks (log rotation, database cleanup)
+additional units are required.
+
+## Inetd-like Socket
+
+This is best suited for systems with *low traffic*, if the
+[socket](#socket) approach doesn't work.
+
+For each incoming connection a new Exim instance starts, handling
+exactly this connection and then exits. The listener port is configured
+in the [systemd socket unit](./inetd/exim.socket).
+
+Additional [_queue runner_ timer and service units](#queue-runner) are required.
+
+For regular maintenance tasks (log rotation, database cleanup)
+additional units are required.
+
+## Queue Runner
+
+This is a *timer*, and a service unit which starts Exim queue runner
+processes. This is necessary, as the socket activated Exim instances
+(from [socket](#socket) and [inetd](#inetd-like-socket))
+do not care once the first delivery attempt is done.
+
+## Maintenance
+
+This is a *timer* and triggers regular cleanup tasks.
+For security it is recommended to use the `User=` Systemd directive in a
+local override file.