Someone should create something like Grammarly or Medium's community-editor feature, for email campaigns. "Before you hit send, get a first impression on your campaign from 10 random beta readers from our community." Then give the beta-readers a prominent "this looks like spam" button to press.
Probably it wouldn't give any different of a response than a regular spam filter; but I imagine that most ad people will think of "it went into the spam filter" as a technical problem, rather than a problem with their messaging. Whereas, if real humans tell them the campaign looks like spam, maybe they'd listen.
This always seemed like a powerful quote to me, not least because I seem to be able to keep finding new applications for it.
[1]: https://readwrite.com/2014/05/29/jeff-atwood-stack-overflow-...