Github user fsteinle commented on the issue:
https://github.com/apache/zeppelin/pull/3098
@mebelousov: Basically this is not related to emails but to the
userPrincipalName. The principalSuffix parameter makes sense, but doesn't
address this issue. In our case we wanna keep the suffix to be sure it's really
unique. Not all users of the organization are in the same AD branch.---
