Cretaed a new user with a separate inbox - can't figure out how to access it

Cretaed a new user with a separate inbox - can't figure out how to access it

Hello,

I added a user to the account so that I would have a separate inbox for things like forum updates from my website.  I successfully added the user, but now I can't figure out how to access that user's inbox. 

1)  How can I access the new user's inbox?
2) Is there a way I can toggle between the inboxes or become a permitted user over that inbox, as well?  It would be nice to be able to see it, because the other user is fictitious, since it is for forum emails.

Thank you!