Add external exchange mailbox to user via admin portal?

Our company doing a project with a partner. For the duration of the project the partner has created a exchange mailbox and sent me all the access info.

I know how to added the exchange mailbox locally on a PC, however I am wondering if it is possible to add and manage it via http://admin.exchange.microsoft.com to a certain company user account (which would make things easier for me to manage without having to access my colleagues PC directly)

Any help/suggestion is much appreciated