Modern email providers, especially ones offered by ISPs often have the same problems that people criticize self-hosted providers for. Even Google has problems. For example, I regularly order via companies that use Shopify. Now, all of the shopify emails are going straight to spam in Gmail, despite constantly marking them as not spam. (These even pass dmarc/spf/dkim etc, so who knows what's going on here.) Email deliv…
That behaviour is the whole problem. If you use a self hosted or small time email provider you're much less likely to have email blocked or filtered by aggressive anti-not-gmail filters.
Hilarious Gmail addresses send tonnes of spam so filtering by provider doesn't do much there days anyway. But Google insists to continue