We use Mailgun as outbound relay for self-hosted email stack, and no more problem with delivery. As a home user you can even stay within the free tier and never pay a dollar for it.
In the Android app, switch from one player to another, from internal to the web player in the settings. It solves the 5.1 playback issue. (Of course, it introduces others, eg. manual screen brightness but it's not as a big issue as no sound.)