You have some really good points that I wasn't able to comment on my original post as I hit the character limit; I think the service-status-api-thing that you are suggesting is a good idea. I could send myself emails which are on the safe-sender list as you are saying so that it is guaranteed not to be marked as spam, and then check the most recently received email's date and then use that.

To check regional availability, I could make multiple email accounts in different regions as there are data residency requirements and so the email accounts would be forced to be in those regions. The issue is that gmail/outlook/hotmail/other providers might get suspicious as I have to use my phone number for verification each time, especially since I'd be creating 20+ accounts.