This is a disingenuous response. You suggest SMTP client submission, but this is being deprecated. Additionally, for small environments, there are situations where the public IP is dynamic, so SMTP relay is not an option.
HVE has been advertised as a replacement for SMTP auth and adding this billing requirement a mere 2 months before it goes live is quite infuriating.
We are an MSP with many small business clients and are already using HVE (as we phaseout SMTP auth) as a last-resort solution for situations that will typically have 100 or fewer email deliveries per month. Setting up an Azure subscription and PAYGO billing for what will end up being a $0.00 bill is a complete waste of time and effort.
Why not just make the first X recipient deliveries free and then, if that limit is approached with no billing policy set, prepend a warning with subsequent deliveries that deliveries will stop working when the limit is reached?