A sales person from Microsoft emails us every 3-6 months or so trying to upsell us on a more expensive 365 subscription. I think their time would be well spent

A sales person from Microsoft emails us every 3-6 months or so trying to upsell us on a more expensive 365 subscription. I think their time would be well spent contacting a customer who hasn't paid. Blocking sending email would also be a more reasonable step before blocking receiving email. And yes, I'd consider moving.