Had the exact same experience when I worked at a non-profit: we had a self-hosted Postfix server, and our subscriber emails would get silently dropped. This only ever happened for Outlook.com users, and we had set up SPF, DKIM, and DMARC long ago. We got the same run-around with Microsoft support, and eventually we had to give up and move to using Google's SMTP Relay service.
It’s tacit collusion between the big providers to force all businesses onto their overpriced cloud services. One Office 365 user costs the same as 50 users at a shared host.
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Had the exact same experience when I worked at a non-profit: we had a self-hosted Postfix server, and our subscriber emails would get silently dropped. This only ever happened for Outlook.com users, and we had set up SPF, DKIM, and DMARC long ago. We got the same run-around with Microsoft support, and eventually we had to give up and move to using Google's SMTP Relay service.
It’s tacit collusion between the big providers to force all businesses onto their overpriced cloud services. One Office 365 user costs the same as 50 users at a shared host.