Microsoft is the only mail provider that exhibits this behiavor. And I've heard the same thing from other people using small domains. The Microsoft autobot response a few years ago said "the domain didn't send enough emails." I don't know why I would send more emails to a provider which doesn't deliver them. Maybe Microsoft has reasons, but no customer service answer. Gmail, Yahoo, and others don't have a problem. Maybe Microsoft allows your small domain as an exception? In the mean time, use Gmail or another cloud provider to get your email. On Tue, 19 Mar 2024, John R. Levine wrote:
Yep, just had another one. Email to local election office silently vanishes because it uses Office365 Cloud email.
I believe they're throwing your mail away, but it's not just because you're small. Like I said, I'm just as small and my mail gets there OK.