Remove trailing whitespace.
diff --git a/Doc/library/mailbox.rst b/Doc/library/mailbox.rst
index 0a8c6df..01d3f4b 100644
--- a/Doc/library/mailbox.rst
+++ b/Doc/library/mailbox.rst
@@ -1686,7 +1686,7 @@
                # that's better than losing a message completely.
                box.lock()
                box.add(message)
-               box.flush()         
+               box.flush()
                box.unlock()
 
                # Remove original message