Manage Microsoft Accounts in Outlook.com

I have two Microsoft accounts.  The first was set up for Microsoft Passport, which no longer exists.  This account will work if I try to sign into support services, but will not be accepted as an Outlook.com account.  The second account is an Outlook.com account.  The email address for the first account is the one I have used for many years, so I would like to use it as an alias in Outlook.com.  When I try to set it up that way, Outlook.com reports that it can't be used because it's signed on as an Office 365 account.  So I went to Office365 and tried to sign on using that account, but Office365 reports that the account doesn't exist.  How can I set up the first account as an alias on Outlook.com?  I want to use it in the "from" field on my Outlook emails.  Any help would be appreciated.