diff --git a/lib/mail.sh b/lib/mail.sh
index 66d9bb9..a7f9040 100644
--- a/lib/mail.sh
+++ b/lib/mail.sh
@@ -169,7 +169,7 @@ plugin {
   # deprecated imapflags extension in addition to all extensions were already
   # enabled by default.
   #sieve_extensions = +notify +imapflags
-  sieve_extensions = +notify +imapflags +vnd.dovecot.pipe +vnd.dovecot.filter
+  sieve_extensions = +notify +imapflags +special-use +vnd.dovecot.pipe +vnd.dovecot.filter
 
   # Which Sieve language extensions are ONLY available in global scripts. This
   # can be used to restrict the use of certain Sieve extensions to administrator