Backport 58594:
Issue #1307, patch by Derek Shockey.
When "MAIL" is received without args, an exception happens instead of
sending a 501 syntax error response.
diff --git a/Misc/NEWS b/Misc/NEWS
index a391219..4cc936d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -32,6 +32,8 @@
 Library
 -------
 
+- Bug #1307: Fix smtpd so it doesn't raise an exception when there is no arg.
+
 - ctypes will now work correctly on 32-bit systems when Python is
   configured with --with-system-ffi.