GH-90: Forwarded messages are not displaying properly on the receivers side

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When the system forwards email it attaches the original email as an inline attachment.

It appears to be somewhat parsed in that we get the headers in but the email appears to be base64 encoded and is just a big block of letters.. sometimes parseable sometimes not.

mhshow, a paragon of ancient history, complains: mhshow: message/rfc822" type in message 8614 should be encoded in 7bit or 8bit

NOTE: closes GH-90

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Okay, so even if we send email that seems to be properly formatted, postmark is re-writing it to base64 encode the message (instead of leaving it as Content-Transfer-Encoding: 8bit)

So postmark is likely getting in the way here. Maybe we need to 'forward' the message by adding text to the text/plain and text/html parts.