Hi Michev and Eric Yin,
Thanks for you messages, I was not able to find the user using eDiscovery or Powershell. However, I was able to find the emails sent from the user account and received by them. As I was not able to locate the user on eDiscovey search, I added their email manually and ran the search. I believed this is because of our recent migration to Office 365, may be the user never had an account in O365. Anyhow, I got what I was looking. Thanks
Appreciate your support.
Thanks
Nick