So, for a short period, the customer will access BC through the fallback domain x.onmicrosoft.com.
The issue is with the SMTP setup.
How can I ensure that the SMTP setup of the BC environment residing on the x.onmicrosoft.com tenant can send emails using the company.com domain, which in the meantime has been moved to the new 365 tenant?
I tried setting up an account with OAUTH authentication, but it doesn't work. The official documentation is vague, and it seems that this type of configuration may only be used by the On-premise versions of BC.
Any ideas?