#11116: roll back on error during add so mailbox isn't left corrupted.
diff --git a/Misc/NEWS b/Misc/NEWS
index f57ba38..a73e102 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -22,6 +22,9 @@
 Library
 -------
 
+- Issue #11116: any error during addition of a message to a mailbox now causes
+  a rollback, instead of leaving the mailbox partially modified.
+
 - Issue #11132: Fix passing of "optimize" parameter when recursing
   in compileall.compile_dir().