"Port" the fix for issue 1974 from the trunk (2.7). Because Python 3.x does things much better, less changes are necessary.
This also shoves test_email_codecs_rename.py onto test_email_codecs.py even though the test needs to be ported to Python 3.
diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index ada14df..2b4d182 100644
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -138,7 +138,7 @@
else:
# Header's got lots of smarts, so use it.
header = Header(v, maxlinelen=self._maxheaderlen,
- header_name=h, continuation_ws='\t')
+ header_name=h)
print(header.encode(), file=self._fp)
# A blank line always separates headers from body
print(file=self._fp)