+# the actual maildir is stored within each snapshot directory.
+#
+# The basic algorithm is to rsync each maildir individually,
+# and to use hard links for retaining historical data.
+#
+# We handle each maildir individually because it becomes very
+# unweldy to hardlink and rsync many hundreds of thousands
+# of files at once. It is much faster to take on smaller
+# chunks at a time.
+#
+# For the backup rotation to work, destuser must be able to run
+# arbitrary bash commands on the desthost.
+#
+# Any maildir which is deleted from the source will be moved to
+# "deleted" directory in the destination. It is up to you to
+# periodically remove this directory or old maildirs in it.