Ref T7199. These were a bad idea which got copy-pasted a bunch.
- There is zero reason to ever set these to different things.
- Unsurprisingly, I don't know of any install which has them set to different things.
Unless I've completely forgotten about it, this option was not motivated by some obscure business need, it was just a bad decision which didn't catch anyone's attention at the time.
We partially remedied the mistake at some point by introducing metamta.reply-handler-domain, which works as a default for all applications, but never cleaned this mess up.