+#
+# The basic algorithm is to rsync each maildir individually,
+# and to use hard links for retaining historical data.
+#
+# We rsync each maildir individually because it becomes very
+# unweldy to start a single rsync of many hundreds of thousands
+# of files.
+#
+# For the backup rotation to work, destuser must be able to run
+# arbitrary bash commands on the desthost.
+#