mailpipe: clarify the source of missing `Return-Path` (bad email)

diff --git a/pygrader/mailpipe.py b/pygrader/mailpipe.py
index f32c1514acf9d3f94ab5f88ff180fbb6515aed3e..bb89144e314ce77bf67c85e406289417b1ea4772 100644 (file)
--- a/pygrader/mailpipe.py
+++ b/pygrader/mailpipe.py
@@ -155,8 +155,9 @@ def mailpipe(basedir, course, stream=None, mailbox=None, input_=None,
     You can send receipts to the acknowledge incoming messages, which
     includes warnings about dropped messages (except for messages
     without ``Return-Path`` and messages where the ``Return-Path``
-    email belongs to multiple ``People``.  Both of these cases should
-    only come from problems with pygrader configuration).
+    email belongs to multiple ``People``.  The former should only
+    occur with malicious emails, and the latter with improper pygrader
+    configurations).
 
     Response to a successful submission: