Scenario: Business Central is on a client's tenant. In their main company, they use Current User as email solution which works fine. The client has another, already existent, company that they've decided to migrate to Business Central in their current BC tenant (just an addition of a new company), but this company already has an existing Microsoft365 tenant. This new company wants to send emails out of BC from their own domain and email addresses. SMTP email would have been the solution, as it has been down the years, but now it is not possible due to the deprecation of Basic Authentication. OAuth2 does not work if it is related to another tenant. Current user won't be any good for obvious reasons (it will send emails from their main company's email addresses instead of this new company's domain). Either bring back Basic Authentication or put in place a new solution that will facilitate a multi tenant scenario such as this, on the email front. The only solution I've managed to make work is to use an external SMTP provider and to mask sending email address to the domain. But this is not ideal.