I have a user that transferred from company A that still needs to use his existing laptop. His laptop is still joined to company A's domain and he still needs to access its Exchange server. I have added his new email account from company B to his existing Outlook 2010 profile. He can receive and send email with company A and company B within the same Outlook profile.
When he tries to Plan a Meeting in Outlook he can't see the schedules of the users at company B but he still see the schedules of the users at company A.