I have just made an attempt to answer a forum post directly from my mail account. The post was - according to the post by mail message - successfully added, however it was empty. My answer qouted the message from Moodle and was send as html. Is this a bug that should be reported, or a setting that should be altered?
That sounds like a bug. Could you please raise an issue for it detailing the e-mail client and version that you're using.
The issue was already in the tracker, see MDL-57955
And I have added MDL-59006
This reply use html.