You're describing one of the solutions made by Ironport, "Bonded Sender". Their solutions were sold to Return Path and Cisco later bought them out, presumably with the bonded sended solution still belonging to Return Path? [1,2]

I've never seen discussion of this in the mainstream though... so I'm not sure if it's actually being used or just shelved.

At this point, I think any proprietary they've created is game for usage. But it's very hard to get multiple large organizations to adopt this.

I definitely think it's a solution.

[1] https://archive.ph/CH98s [2] https://www.computerworld.com/article/2548788/cisco-to-acqui...