Warn before sending message that has Markdown (or was converted during compose)

[abackstrom]

Oftentimes in Gmail I will compose a message in Markdown, using Markdown Here along the way to check formatting, then accidentally send the message in its unformatted state. I use the Gmail "Undo Send" feature to abort the send, trigger the Markdown Here shortcut, and resend. Unfortunately, this is not so simple in Thunderbird.

Could Markdown Here warn me when it thinks I'm sending a Markdown-formatted message as text?

[adam-p]

Duplicate of #90. And yeah, I do that all the time too.