The HTML Emails that are generated can show markup in them. I’m creating this thread in reference to a bug that was reported some time ago in another thread.
If the recipient’s mail client is set to accept HTML email, the plugin works as expected, however, if the recipient’s mail client is set to only accept plaintext (ie, non-HTML) email, then all the HTML markup will be rendered in the message as though it were text. To recreate: send yourself an email with the plugin, then view is as an HTML message (looks fine) then view it as a plaintext message (shows markup). This can be fixed in the send_mail() function.