it's known that google doesn't want you to use email, they want you to use gmail. same as how all those fucks co-opt standard protocols (XMPP, ActivityPub, etc.) and then defederate it and make it their own walled, proprietary thing.

I ran a slew of geo-dispersed mail servers for a decade+; not really spam as it's willing recipients but essentially not that far from it, either. also fully compliant, experimenting with voodoo-adjacent tips for improving deliverability (none of them work). so glad to be out of that racket.

anyhoo, you can utilise mailchimp/sendinblue/etc as they have a direct pipe into gmail/outlook infra and are not subject to any of those harassment tactics, which is basically payola. the prices last time I was involved with checking things weren't that much better (worse in fact, if you add the costs of running all that shit) than transferring everything to gmail and friends, which is their ultimate goal.