[3.14] gh-124864: Extends smtplib documentation on ESMTP options format (GH-132547) (#142796)

Co-authored-by: Patrick R <[email protected]>

Author: miss-islington

Doc/library/smtplib.rst

@@ -440,9 +440,11 @@ An :class:`SMTP` instance has the following methods:
    Send mail.  The required arguments are an :rfc:`822` from-address string, a list
    of :rfc:`822` to-address strings (a bare string will be treated as a list with 1
    address), and a message string.  The caller may pass a list of ESMTP options
-   (such as ``8bitmime``) to be used in ``MAIL FROM`` commands as *mail_options*.
+   (such as ``"8bitmime"``) to be used in ``MAIL FROM`` commands as *mail_options*.
    ESMTP options (such as ``DSN`` commands) that should be used with all ``RCPT``
-   commands can be passed as *rcpt_options*.  (If you need to use different ESMTP
+   commands can be passed as *rcpt_options*. Each option should be passed as a string
+   containing the full text of the option, including any potential key
+   (for instance, ``"NOTIFY=SUCCESS,FAILURE"``). (If you need to use different ESMTP
    options to different recipients you have to use the low-level methods such as
    :meth:`!mail`, :meth:`!rcpt` and :meth:`!data` to send the message.)