[issue21991] The new email API should use MappingProxyType instead of returning new dicts.

[Roundup Robot]

Roundup Robot added the comment:

New changeset fea3ddcaf652 by R David Murray in branch '3.4':
#21991: make headerregistry params property MappingProxyType.
https://hg.python.org/cpython/rev/fea3ddcaf652

New changeset 5beb1ea76f36 by R David Murray in branch 'default':
Merge: #21991: make headerregistry params property MappingProxyType.
https://hg.python.org/cpython/rev/5beb1ea76f36

----------
nosy: +python-dev

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21991>
_______________________________________