Implementing Inbound SMTP DANE with DNSSEC for Exchange Online Mail Flow

bogdanst95 During the public preview, the old record will be maintained to ease the preview experience. But for the GA we will implement a mechanism to ensure the 'old' record is healthy only for a specific period and then deleted, as we've been getting similar feedback that there needs to be a transition period where both are working - is there a specific time window you would prefer (8 hours? 24 hours? 48 hours? 1 week?)? 

Customers will use powershell to enable DNSSEC, which will provision the new record and provide the customer their new MX value. For GA, this is when the timeline for the deprovisioning of the old MX would begin. If a customer's MX is pointing to their 3rd party relay, then the 3rd party relays to EXO, the customer will update the target host for the 3rd party relay