After your new 365 mailbox has been setup, you need to re-configure Outlook to add the account into a new profile. Here’s how:
Start by clicking File in the top left of Outlook.
In the Account Information tab, click the Account Settings dropdown and then Manage Profiles.
The Mail Setup box should now pop up. Click Show Profiles…
Click Add… to create a new profile and name it “365”. Then click OK.
Enter your Name, Email Address and Password into the relevant boxes and click Next.
It will now configure the account, it may pop up with Windows Security asking you to re-enter the password (click Remember my credentials to avoid re-entering this later). Click OK, then Next. Click Finish on the next page.
Once you are brought back the Mail prompt. From the dropdown, select 365. Click Apply and then OK. Close outlook and re-open.
Now you should be all set with your new Office 365 email.