After the first leaks concerning build 10051 of the Windows 10 emerged with a purported changelog, the next materials to appear are the first screenshots of the new Mail and Calendar apps. The earlier leak showed tiles present for each, but this is the first look at them 'in the wild.'
It also further serves to suggest we will in fact get our hands on them in the next build. Considering we only just saw build 10049 in the fast ring with Project Spartan, as well as the first look at the new Music and Video apps, it's clear Microsoft is beginning to step up the features at a significant rate.
For now, we sit and wait.