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

[Lita Cho]

Lita Cho added the comment:

Hi David, I can take this on as I am learning the email api currently.

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nosy: +Lita.Cho

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