To add a Microsoft 365 Email account to Outlook 365, follow these steps:
In Outlook 365, click on File > Account Settings > Account Settings
Then under the Email tab, click on New
Now Microsoft Outlook will search for a Microsoft email account in case you have signed in previously with one
If the search finds your Microsoft email account, click on Connect
Otherwise, type in your Microsoft email account and then click on Connect
Now you will be prompted to Enter password, then click on Sign in
Now this part is one of the most important parts of the setup with the Microsoft Office 365 email setup.
Allow my organization to manage my device should be ticked
Microsoft 365 Email Essentials or Microsoft 365 Business Email accounts, click This app only
Microsoft 365 Business Premium, click Yes
IMPORTANT: If unsure what Microsoft 365 email account you have, click on This app only to be safe.
The Microsoft 365 email account will now be added to Outlook 365 and when complete, you will be prompted to Add another email address or click Done if this is the only email address you are adding to Outlook.
NOTE: If you want to also setup the Microsoft 365 email account on your mobile, leave the Set up Outlook Mobile on my phone, too ticked
Microsoft Outlook 365 will now open and you have successfully setup your email account.