bpo-31887: Adds documentations for special multipart/signed handling (GH-4268)
This pull request adds some information about the special multipart/signed handling to clear about disabling header folding.
https://bugs.python.org/issue31887
diff --git a/Doc/library/email.generator.rst b/Doc/library/email.generator.rst
index 2575a51..fc535a3 100644
--- a/Doc/library/email.generator.rst
+++ b/Doc/library/email.generator.rst
@@ -36,6 +36,10 @@
Content Transfer Encoding techniques for encoding email messages for transport
over channels that are not "8 bit clean".
+To accomodate reproducible processing of SMIME-signed messages
+:class:`Generator` disables header folding for message parts of type
+``multipart/signed`` and all subparts.
+
.. class:: BytesGenerator(outfp, mangle_from_=None, maxheaderlen=None, *, \
policy=None)