diff --git a/README.md b/README.md
index d14ea70..5deb19a 100644
--- a/README.md
+++ b/README.md
@@ -6,8 +6,16 @@ provides histogram metrics for the size and age of messages stored in
 the mail queue. It extracts these metrics from Postfix by connecting to
 a UNIX socket under `/var/spool`.
 
-In addition to that, it counts events by parsing Postfix's log file,
-using regular expression matching. It truncates the log file when
+In addition to that, it counts events by parsing Postfix's log entries,
+using regular expression matching.
+The log entries are retrieved from the systemd journal or from a log file.
+
+Please refer to this utility's `main()` function for a list of supported
+command line flags.
+
+## Events from log file
+
+The log file is truncated when
 processed, so that the next iteration doesn't interpret the same lines
 twice. It makes sense to configure your syslogger to multiplex log
 entries to a second file:
@@ -16,8 +24,11 @@ entries to a second file:
 mail.* -/var/log/postfix_exporter_input.log
 ```
 
-There is also an option to collect the metrics via the systemd journal instead of a log file.
+The path to the log file is specified with the `-postfix.logfile_path` flag.
 
+## Events from systemd
 
-Please refer to this utility's `main()` function for a list of supported
-command line flags.
+Retrieval from the systemd journal is enabled with the `-systemd.enable` flag.
+This overrides the log file setting.
+It is possible to specify the unit (with `-systemd.unit`) or slice (with `-systemd.slice`).
+Additionally, it is possible to read the journal from a directory with the `-systemd.journal_path` flag.