diff -r a377a4298b4e Lib/email/generator.py
--- a/Lib/email/generator.py	Wed Aug 22 23:27:26 2012 -0700
+++ b/Lib/email/generator.py	Fri Aug 24 02:06:32 2012 +0800
@@ -391,6 +391,8 @@
         if msg._payload is None:
             return
         if _has_surrogates(msg._payload):
+            if self._mangle_from_:
+                msg._payload = fcre.sub(">From ", msg._payload)
             self.write(msg._payload)
         else:
             super(BytesGenerator,self)._handle_text(msg)