Really? I just looked at Microsoft 365 pricing, and it comes with Outlook Premium.
https://support.microsoft.com/en-us/office/get-a-personalize...
https://support.microsoft.com/en-us/office/get-a-personalize...
> To continue using a personalized email address and custom domains with Outlook.com, you will need to subscribe to Microsoft 365. Learn more about Premium features in Outlook.com for Microsoft 365 subscribers.
From: https://support.microsoft.com/en-us/office/premium-features-...
Which causes a price increase.