Two e-mail accounts not able to open both at same time with the new Outlook

I use to be able to click in the right side and toggle between the two accounts, this feature is no longer available and I can not log on to the accounts at the same time now.  I tried linking them and having the one account send only but no one was receiving my e-mailes from the linked account until hours after they were sent!  Help I hate this new format, and am about to start over with a new e-mail service!