Thanks everyone, and appreciate breaking this out to its own topic.
@JammyDodger that def. sounds like it would do the trick, and @pfaffman sounds like he’s right on the money with how I could handle my domain + subdomain setup.
If anyone is curious, the subdomain is what Mailgun suggests as best practice if you already have email on your domain handled by another entity (Google Apps, in our case).
tl;dr Email remains very hard.