diff -r 4803a6d569f7 Lib/smtplib.py
--- a/Lib/smtplib.py	Mon Apr 27 17:49:16 2015 +0300
+++ b/Lib/smtplib.py	Mon Apr 27 23:57:27 2015 +0300
@@ -52,6 +52,7 @@
 import copy
 import datetime
 import sys
+from itertools import chain
 from email.base64mime import body_encode as encode_base64
 
 __all__ = ["SMTPException", "SMTPServerDisconnected", "SMTPResponseException",
@@ -868,10 +869,8 @@
                            if (header_prefix + 'Sender') in msg
                            else msg[header_prefix + 'From'])
         if to_addrs is None:
-            addr_fields = [f for f in (msg[header_prefix + 'To'],
-                                       msg[header_prefix + 'Bcc'],
-                                       msg[header_prefix + 'Cc']) if f is not None]
-            to_addrs = [a[1] for a in email.utils.getaddresses(addr_fields)]
+            addr_fields = [msg.get_all(f, []) for f in ('To', 'Bcc', 'Cc')]
+            to_addrs = [a[1] for a in email.utils.getaddresses(chain(*addr_fields))]
         # Make a local copy so we can delete the bcc headers.
         msg_copy = copy.copy(msg)
         del msg_copy['Bcc']