Odd Issue with Forwarded Messages, Empty Message at Top

[cmiles74]

First, thank you for a great package! The younger people I work with have been complaining recently about how my email messages "do not look so great visually" and have been asking what the ">" symbol before text means. Now with this package they think I'm using a web-based mailer or maybe even Apple Mail! 😎

When I reply to messages everything works well; the recipient gets my new message at the top and they can read the prior messages at the bottom.

When I forward a message, it looks fine inside Emacs but when the recipient views the message in GMail, there's an empty bit at the top; I suspect that this is where the plain text version of the message might go. Maybe this shouldn't be visible at all in GMail, perhaps that's why it appears empty.

Here's a screenshot of me editing a forwarded message. Apologies for the content, I was trying to figure out which combination of features was causing the issue!

When this message is sent, it looks like the image below in GMail.

Much to my surprise, the same issue is visible in Emacs (I'm using Notmuch).

I'm only so-so with the Elisp but if you have an idea of where the problem might lie, I'd happy to take a stab at fixing it and submitting a PR.