After five months of use, I have decided I hate the iOS 10 mail app and despise the mindset behind it. The threaded discussions are just unusable. Totally unusable.
I had an irate customer ring the other day about an email he had just received being different to the commitments made the previous day. I just knew straight away even before I asked he was reading from an iPhone and looking at a threaded email trail. Sure enough, the email he had gotten upset about was from two years ago about a two year old project, not the current one.
This is not acceptable, an example of pointless fiddling with a system that was working, everyone understood how it worked because it was universal, and it wasn't broke.
As it is set up in default now, the mail app is unintuitive and hard to use. Accessing email on an iPhone should be quick and so easy to understand you don't have to think about what you are doing. Ios10 is trying to change how users interact with email threads.
Whoever the wankers were that a) designed the ioS10 mail UI, and b) approved it need to be lined up against a wall to have ridicule and rotten fruit hurled at them.