diff --git a/mail-compress b/mail-compress
index 5624bd1..29dc27f 100755
--- a/mail-compress
+++ b/mail-compress
@@ -34,7 +34,7 @@ require 'pathname'
 require 'set'
 
 def maildirlock path
-	return yield # currently deactivated, maildirlock does not work
+	return yield # currently deactivated
 	io = IO.popen ['/usr/lib/dovecot/maildirlock', path.to_s, '10'], out: %i[child out]
 	lockpidfile = Pathname.new io.read
 	pid, pst = Process.wait2
@@ -99,7 +99,18 @@ def unxz mf, tf
 	if 0 == pst.exitstatus
 		true
 	else
-		log "  Compression failed for: #{mf}"
+		log "  Decompression [xz] failed for: #{mf}"
+		false
+	end
+end
+
+def unzstd mf, tf
+	pid = Process.spawn 'zstd', '-d', umask: 0177, in: mf.to_s, out: tf.to_s, close_others: true
+	_pid, pst = Process.waitpid2( pid)
+	if 0 == pst.exitstatus
+		true
+	else
+		log "  Decompression [zstd] failed for: #{mf}"
 		false
 	end
 end
@@ -230,6 +241,20 @@ def process xf
 		end
 	end
 
+	if false and :zst == fs
+		nf = mf.new compressed: false
+		tf = nf.new dir: :tmp
+		return log "  Uncompressed mail already exist: #{nf}"  if nf.exist?
+		return log "  Temporary file already exist: #{tf}"  if tf.exist?
+		STDERR.print "<\r"
+		return  unless unzstd mf.to_s, tf.to_s
+		STDERR.print "<<\r"
+		restat tf, stat
+		place mf, nf, tf
+		STDERR.print "<<<\r"
+		return process(nf)
+	end
+
 	if :xz == fs
 		nf = mf.new compressed: false
 		tf = nf.new dir: :tmp