commit bd5cdd5f2ddf4e9c26ff9353d15324dd0bbda37c
Author: Jeremy Harris <jgh146exb@wizmail.org>
Date:   Mon Feb 12 17:29:22 2018 +0000

    ACL: Enforce non-usability of control=utf8_downconvert in MAIL ACL.  Bug 2239

diff --git a/src/src/acl.c b/src/src/acl.c
index 750fd2da..95ee2667 100644
--- a/src/src/acl.c
+++ b/src/src/acl.c
@@ -533,7 +533,9 @@ static control_def controls_list[] = {
   },
 #ifdef SUPPORT_I18N
 [CONTROL_UTF8_DOWNCONVERT] =
-  { US"utf8_downconvert",        TRUE, 0 }
+  { US"utf8_downconvert",        TRUE,
+    (unsigned) ~((1<<ACL_WHERE_RCPT) | (1<<ACL_WHERE_VRFY))
+  }
 #endif
 };