You can click through to the commenter's profile https://news.ycombinator.com/user?id=crubier https://news.ycombinator.com/user?id=crubier and from there you ca

You can click through to the commenter's profile https://news.ycombinator.com/user?id=crubier https://news.ycombinator.com/user?id=crubier and from there you can find their Twitter and GitHub profiles (which contains their email). Alternatively, since they also went through YCS18 as Sterblue, you could use YC's internal BookFace platform to ask for an introduction.