One of the theories linking Seth Rich to Wikileaks is that his positon as Voter Expansion Data Director gave him access to the DNC server and it would be easy for him to download emails and not be detected.
Having worked in IT, I can say pretty confidently that only System Administrators have privileges to access Mail Servers. Any Sys Admin who would grant server access to unauthorized people in an organization would be fired.
Seth’s job at the DNC had nothing to do with servers.
Here are several articles that describe the reason his job was created.
https://medium.com/@MeanJean/what-is-the-dnc-voter-expansion-project-264395c439f3
Even if he magically could access every employees inbox, why pick just 10 mid-level DNC staff members vs the top executives such as Debbie Wasserman Schultz or Donna Brazile if he wanted to maximize the damage to Hillary Clinton?
In addition, accessing emails as an administrator would be very easy for Crowdstrike to identify via its monitoring tool Falcon. Falcon was in place during late May 2016 when the emails were extracted.
Disclaimer: I have no inside knowledge on whether Seth Rich or anyone in his family was involved in the leak of the DNC emails. My analysis is based on various YouTube videos, social media posts, court cases, and other published articles.