Is it possible to backup different O365 accounts with the same media agent?
or do you need 1 media agent per O365 account?
Could you please clarify what you mean here? You can back up multiple O365 accounts from one Exchange Mailbox agent as long as the service account has access to them. Do you mean use multiple service accounts on one Exchange Mailbox agent? Currently that is not possible though you could multi instance (install more then one exchange mailbox agent on the same server) to possibly achieve this.