#12147: make send_message correctly handle Sender and Resent- headers.
Original patch by Nicolas Estibals. My tweaks to the patch were mostly
style/cosmetic, and adding more tests.
diff --git a/Doc/library/smtplib.rst b/Doc/library/smtplib.rst
index 531a64d..5978a8f 100644
--- a/Doc/library/smtplib.rst
+++ b/Doc/library/smtplib.rst
@@ -323,21 +323,32 @@
.. versionchanged:: 3.2 *msg* may be a byte string.
-.. method:: SMTP.send_message(msg, from_addr=None, to_addrs=None, mail_options=[], rcpt_options=[])
+.. method:: SMTP.send_message(msg, from_addr=None, to_addrs=None, \
+ mail_options=[], rcpt_options=[])
This is a convenience method for calling :meth:`sendmail` with the message
represented by an :class:`email.message.Message` object. The arguments have
the same meaning as for :meth:`sendmail`, except that *msg* is a ``Message``
object.
- If *from_addr* is ``None``, ``send_message`` sets its value to the value of
- the :mailheader:`From` header from *msg*. If *to_addrs* is ``None``,
- ``send_message`` combines the values (if any) of the :mailheader:`To`,
- :mailheader:`CC`, and :mailheader:`Bcc` fields from *msg*. Regardless of
- the values of *from_addr* and *to_addrs*, ``send_message`` deletes any Bcc
- field from *msg*. It then serializes *msg* using
+ If *from_addr* is ``None`` or *to_addrs* is ``None``, ``send_message`` fills
+ those arguments with addresses extracted from the headers of *msg* as
+ specified in :rfc:`2822`\: *from_addr* is set to the :mailheader:`Sender`
+ field if it is present, and otherwise to the :mailheader:`From` field.
+ *to_adresses* combines the values (if any) of the :mailheader:`To`,
+ :mailheader:`Cc`, and :mailheader:`Bcc` fields from *msg*. If exactly one
+ set of :mailheader:`Resent-*` headers appear in the message, the regular
+ headers are ignored and the :mailheader:`Resent-*` headers are used instead.
+ If the message contains more than one set of :mailheader:`Resent-*` headers,
+ a :exc:`ValueError` is raised, since there is no way to unambiguously detect
+ the most recent set of :mailheader:`Resent-` headers.
+
+ ``send_message`` serializes *msg* using
:class:`~email.generator.BytesGenerator` with ``\r\n`` as the *linesep*, and
- calls :meth:`sendmail` to transmit the resulting message.
+ calls :meth:`sendmail` to transmit the resulting message. Regardless of the
+ values of *from_addr* and *to_addrs*, ``send_message`` does not transmit any
+ :mailheader:`Bcc` or :mailheader:`Resent-Bcc` headers that may appear
+ in *msg*.
.. versionadded:: 3.2