Apart from using the latest V9 release as @Gary advised, if you type in your usual email address in the wizard and it won’t accept it for a Microsoft 365 or Exchange Domain account, it could be that you eg: might need to use a “.onmicrosft address” to start in the wizard instead of your actual email address as @Simon9 posted in the thread below.
A onmicrosoft.com account is a domain name that Microsoft creates for a company or school that signs up for an Office 365 for Business subscription.
https://forum.emclient.com/t/emclient-wont-activate-my-exchange-account/92150/20
(Quote Extract posts from Simon9)
“emClient requires .onmicrosoft address to start”
“It forms the login name for the Microsoft account, for 365 and for exchange server, but it is not my e-mail address”.