Outlook/Hotmail servers blocking perceived spam

I subscribe to several emails from @dearreader.com. Periodically, they stop coming. Sometimes I can resubscribe, sometimes not. The technical folks at dearreader.com tell me that Outlook/Hotmail are blocking delivery of their emails as perceived spam, an on-going problem for all their Outlook subscribers. They're not spam, they are subscriptions, I asked for them. They suggested I use gmail or another provider to get better delivery.