diff -r 8d2b62d716b0 -r 106402245301 mercurial/mail.py
--- a/mercurial/mail.py	Tue Apr 20 20:35:46 2021 +0200
+++ b/mercurial/mail.py	Tue Apr 20 23:31:36 2021 -0400
@@ -220,6 +220,7 @@
 
 def _mbox(mbox, sender, recipients, msg):
     '''write mails to mbox'''
+    # TODO: use python mbox library for proper locking
     with open(mbox, b'ab+') as fp:
         # Should be time.asctime(), but Windows prints 2-characters day
         # of month instead of one. Make them print the same thing.