Mailsuite

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- Fix `publicsuffix2` warning

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- Pin `mail-parser` version at `3.15.0` due to a parsing regression in `4.0.0`

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- Fix IMAP namespace handling (PR 11 closes issue 10)

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- Accept `plain_message=None` when creating emails

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- Fix missing `body_urls` list when an email does not contain an HTML body

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- Email parsing improvements
- Parse out email addresses in the `Delivered-To` header
- Rename `reply_to` key to `reply-to`
- Replaces formatting provided by `mailparser` with parsed out email addresses that match the rest of the output