1 files changed, 4 insertions, 0 deletions
diff --git a/Misc/NEWS b/Misc/NEWS
index 1aca6e7..4316b75 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -181,6 +181,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #21991: Make email.headerregistry's header 'params' attributes
+  be read-only (MappingProxyType).  Previously the dictionary was modifiable
+  but a new one was created on each access of the attribute.
+
 - Issue #22638: SSLv3 is now disabled throughout the standard library.
   It can still be enabled by instantiating a SSLContext manually.