I wasn't sure how to do toname and replyto because of the way the it opts to not use the to and uses headers if it has an attached file, hopefully someone else can add those.
Added from name for mail api call
Just scanning through this code, I think it looks pretty thorough, but it's missing a small piece. . You've updated the Web library, but not the corresponding SMTP library. In order to get a feature into the this library, we'd like to have it work across both platforms.
For this particular SMTP library, we use a third party library called Swift Mailer. Here's some documentation that will guide you in the right direction : http://swiftmailer.org/docs/messages.html. If you can get that working, we'll push it through our QA review.
Thanks for taking the initiative here!
This was fixed by c0da924