--- courier/imapd.rc.in.orig	2018-08-23 13:12:13.000000000 +0200
+++ courier/imapd.rc.in	2020-04-26 13:47:12.593117000 +0200
@@ -30,7 +30,7 @@
 	then
 		rm -f "$TLS_CACHEFILE"
 		touch "$TLS_CACHEFILE"
-		chown @mailuser@ "$TLS_CACHEFILE"
+		/usr/sbin/chown @mailuser@ "$TLS_CACHEFILE"
 		chgrp @mailgroup@  "$TLS_CACHEFILE"
 		chmod 600  "$TLS_CACHEFILE"
 	fi