#24277: The new email API is no longer provisional.

This is a wholesale reorganization and editing of the email documentation to
make the new API the standard one, and the old API the 'legacy' one.  The
default is still the compat32 policy, for backward compatibility.  We will
change that eventually.
diff --git a/Doc/library/email.mime.rst b/Doc/library/email.mime.rst
index 165011d..d9dae9f 100644
--- a/Doc/library/email.mime.rst
+++ b/Doc/library/email.mime.rst
@@ -8,6 +8,11 @@
 
 --------------
 
+This module is part of the legacy (``Compat32``) email API.  Its functionality
+is partially replaced by the :mod:`~email.contentmanager` in the new API, but
+in certain applications these classes may still be useful, even in non-legacy
+code.
+
 Ordinarily, you get a message object structure by passing a file or some text to
 a parser, which parses the text and returns the root message object.  However
 you can also build a complete message structure from scratch, or even individual