Office 365 Exchange Online Plan 1 is great for hosting email on your personal domain. At £36 a year, aka £3 per month you get an enterprise grade Exchange inbox.
However if you have setup your domain in the Microsoft 365 admin center, then try to change the primary email address on your Microsoft Account to an email address hosted with Office 365 Exchange, you are greeted with the following error: “You can’t add a work or school email address as an alias to a personal Microsoft account. Please try another.”
So basically if your paying Microsoft to host email for your personal domain, you then can’t associate your Microsoft account with any email address on that domain, or can you?